全文获取类型
收费全文 | 6482篇 |
免费 | 545篇 |
国内免费 | 5篇 |
专业分类
7032篇 |
出版年
2023年 | 39篇 |
2022年 | 96篇 |
2021年 | 179篇 |
2020年 | 91篇 |
2019年 | 100篇 |
2018年 | 142篇 |
2017年 | 128篇 |
2016年 | 226篇 |
2015年 | 403篇 |
2014年 | 445篇 |
2013年 | 432篇 |
2012年 | 630篇 |
2011年 | 570篇 |
2010年 | 342篇 |
2009年 | 293篇 |
2008年 | 409篇 |
2007年 | 407篇 |
2006年 | 391篇 |
2005年 | 300篇 |
2004年 | 316篇 |
2003年 | 217篇 |
2002年 | 221篇 |
2001年 | 49篇 |
2000年 | 42篇 |
1999年 | 58篇 |
1998年 | 44篇 |
1997年 | 52篇 |
1996年 | 36篇 |
1995年 | 25篇 |
1994年 | 38篇 |
1993年 | 24篇 |
1992年 | 22篇 |
1991年 | 24篇 |
1990年 | 19篇 |
1989年 | 17篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 17篇 |
1983年 | 16篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 13篇 |
1973年 | 9篇 |
1972年 | 8篇 |
1970年 | 7篇 |
排序方式: 共有7032条查询结果,搜索用时 0 毫秒
991.
BACKGROUND: Inflammatory myofibroblastic tumors (IMTs) can vary from benign pseudosarcomatous tumors to low grade sarcomas. To date, fine needle aspiration (FNA) findings of lung IMTs, especially in the aggressive form, have not been fully described. Here we present FNA biopsy findings in conjunction with immunohistochemical studies in a case of primary and recurrent pulmonary IMT. CASE: A 22-year-old man first presented with a left lung mass and 4.5 years later with a recurrent mass. Preoperative computed tomography-guided FNA was performed on both tumors. FNA cytologic smears of both specimens consisted of scant, distorted spindle cells suggestive of a spindle cell lesion but were insufficient for further classification. Needle core biopsies as well as touch imprints were performed during the FNA procedures. The imprints revealed abundant, well-preserved spindle cells with mild to moderate atypia and intermixed lymphocytes and plasma cells. The spindle cells in both specimens were immunoreactive for vimentin and smooth muscle actin and were negative for pancytokeratin, desmin, CD34 and c-kit. Thirty percent of the tumor cells were positive for p53. The findings were compatible with those of IMT. Histologic examination of the surgically resected initial and recurrent masses confirmed the diagnosis of lMT. CONCLUSION: The cytologic findings of pulmonary IMT in FNA specimens are suggestive of, although not specific for, IMT. Immunohistochemical studies can assist in the diagnosis by excluding other spindle cell lesions. Cytologic atypia and p53 immunoreactivity may be indicators of aggressive IMTs. 相似文献
992.
P. Winter T. Pfaff S. M. Udupa B. Hüttel P. C. Sharma S. Sahi R. Arreguin-Espinoza F. Weigand F. J. Muehlbauer G. Kahl 《Molecular & general genetics : MGG》1999,262(1):90-101
A size-selected genomic library comprising 280,000 colonies and representing ≈18% of the chickpea genome, was screened for
(GA)n, (GAA)n and (TAA)n microsatellite-containing clones, of which 389 were sequenced. The majority (∼75%) contained perfect repeats; interrupted,
interrupted compound and compound repeats were only present in 6%–9% of cases. (TAA)-microsatellites contained the longest
repeats, with unit numbers from 9 to 131. For 218 loci primers could be designed and used for the detection of microsatellite
length polymorphisms in six chickpea breeding cultivars, as well as in C. reticulatum and C. echinospermum, wild, intercrossable relatives of chickpea. A total of 174 primer pairs gave interpretable banding patterns, 137 (79%) of
which revealed at least two alleles on native polyacrylamide gels. A total of 120 sequence-tagged microsatellite site (STMS)
markers were genetically mapped in 90 recombinant inbred lines from an inter-species cross between C. reticulatum and the chickpea cultivar ICC 4958. Markers could be arranged in 11 linkage groups (at a LOD score of 4) covering 613 cM.
Clustering as well as random distribution of loci was observed. Segregation of 46 markers (39%) deviated significantly (P ≥ 0.05) from the expected 1:1 ratio. The majority of these loci (73%) were located in three distinct regions of the genome.
The present STMS marker map represents the most advanced co-dominant DNA marker map of the chickpea genome.
Received: 14 January 1999 / Accepted: 29 April 1999 相似文献
993.
A V Capuco S Kahl L J Jack J O Bishop H Wallace 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1999,221(4):345-351
This experiment tested the hypothesis that thyroid hormones are essential for a milk production response to growth hormone (GH) and prolactin (PRL). Prior to breeding, female transgenic mice expressing the herpes simplex type-I thymidine kinase in the thyroid were treated with ganciclovir to ablate thyroid follicular cells. To provide for normal gestation, thyrocyte-ablated mice were supplied thyroxine (T4) in drinking water (0.2 microgram/ml) until 7 days before parturition. Litter size was adjusted to 9 pups, hormone administration began on Day 2 of lactation, and mice were sacrificed on Day 12. There were 5-6 mice in each of 7 treatments that included nonablated controls, thyrocyte-ablated controls, and thyrocyte-ablated mice treated with T4, GH, PRL, GH + T4, and PRL + T4. Thyroxine was administered in drinking water, and GH and PRL (20 microgram/d) were administered by subcutaneous injection. Compared with thyrocyte-ablated controls, litter weight gain was unaffected when dams were treated with GH, PRL, or T4 alone. However, when dams were treated with GH or PRL in combination with T4, litter weight gain increased 13% compared with thyrocyte-ablated controls and 18% compared with GH or PRL-treated mice. Concentration of T4 in serum of pups averaged 62 ng/ml and did not differ among treatments. Concentration of T4 in serum of dams averaged 76 ng/ml when T4-treated. Thyroxine 5'-deiodinase (5'D), the enzyme that converts T4 to triiodothyronine, was quantitated in liver, kidney, and mammary gland. Quantity of 5'D was lower in liver and kidney of thyrocyte-ablated dams without T4 than in respective tissues of mice treated with T4, and there was no effect of GH or PRL. However, in mammary gland, 5'D was increased by treatment with GH, PRL, or T4. Data show that thyroid hormones are necessary for a galactopoietic response to GH and PRL and demonstrate a unique organ-specific regulation of 5'D by galactopoietic hormones. 相似文献
994.
Nathaniel J. Cosper Christina M. V. Stålhandske Ruth E. Saari Robert P. Hausinger R. A. Scott 《Journal of biological inorganic chemistry》1999,4(1):122-129
The first step in the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) by Ralstonia eutropha JMP134 is catalyzed by the α-ketoglutarate (α-KG)-dependent dioxygenase TfdA. Previously, EPR and ESEEM studies on inactive
Cu(II)-substituted TfdA suggested a mixture of nitrogen/oxygen coordination with two imidazole-like ligands. Differences between
the spectra for Cu TfdA and α-KG- and 2,4-D-treated samples were interpreted as a rearrangement of the g–tensor principal axis system. Herein, we report the use of X-ray absorption spectroscopy (XAS) to further characterize the
metal coordination environment of Cu TfdA as well as that in the active, wild-type Fe(II) enzyme. The EXAFS data are interpreted
in terms of four N/O ligands (two imidazole-like) in the Cu TfdA sample and six N/O ligands (one or two imidazole-like) in
the Fe TfdA sample. Addition of α-KG results in no significant structural change in coordination for Cu or Fe TfdA. However,
addition of 2,4-D results in a decrease in the number of imidazole ligands in both Cu and Fe TfdA. Since this change is seen
both in the Fe and Cu EXAFS, loss of one histidine ligand upon 2,4-D addition best describes the phenomenon. These XAS data
clearly demonstrate that changes occur in the atomic environment of the metallocenter upon substrate binding.
Received: 3 July 1998 / Accepted: 13 October 1998 相似文献
995.
Christina Karatzaferi Giannis Giakas Derek Ball 《European journal of applied physiology and occupational physiology》1999,80(5):508-510
Fatigue Profile, a new numerical method for characterising fatigue in isokinetic cycle ergometry is presented and compared with the conventional fatigue index (FI). The new method describes the temporal development of muscle fatigue based on the decline of peak power output throughout a whole trial. The advantage of this method is demonstrated by the analysis of two 25 s maximum trials, separated by 90 s recovery, performed by a well-trained athlete at a pedal frequency of 120 revolutions per minute. A fourth degree polynomial was fitted to model the peak power data. Using the polynomial model coefficients the first derivative represented the rate of changing peak power which represented the Fatigue Profile. The conventional FI was calculated as -35 Ws(-1) and -32 Ws(-1) for trials 1 and 2 respectively, indicating minor differences in fatigue between trials. In contrast the Fatigue Profile revealed important numeric and temporal differences between the trials. For trial 1 a maximum rate of peak power decline of -65 Ws(-1) was reached at approximately 6 s into the trial. In marked contrast, in trial 2, maximum rate of peak power decline (-146 Ws(-1)) occurred immediately. The Fatigue Profile approach allows the characterisation of the temporal development of fatigue under different experimental conditions and in combination with other techniques may yield further insight into the underlying mechanisms of fatigue. 相似文献
996.
997.
Grgory Hammad Mathilde Reyt Nikita Beliy Marion Baillet Michele Deantoni Alexia Lesoinne Vincenzo Muto Christina Schmidt 《PLoS computational biology》2021,17(10)
Over the past 40 years, actigraphy has been used to study rest-activity patterns in circadian rhythm and sleep research. Furthermore, considering its simplicity of use, there is a growing interest in the analysis of large population-based samples, using actigraphy. Here, we introduce pyActigraphy, a comprehensive toolbox for data visualization and analysis including multiple sleep detection algorithms and rest-activity rhythm variables. This open-source python package implements methods to read multiple data formats, quantify various properties of rest-activity rhythms, visualize sleep agendas, automatically detect rest periods and perform more advanced signal processing analyses. The development of this package aims to pave the way towards the establishment of a comprehensive open-source software suite, supported by a community of both developers and researchers, that would provide all the necessary tools for in-depth and large scale actigraphy data analyses. 相似文献
998.
Cyndi Kuehler Alan Lieberman Paul Oesterle Tracey Powers Marla Kuhn Joseph Kuhn Jay Nelson Tom Snetsinger Christina Herrmann Peter Harrity Erik Tweed Steve Fancy Bethany Woodworth Tom Telfer 《Zoo biology》2000,19(4):263-277
From 1995 to 1999, two species of endemic Hawaiian thrushes, `Oma`o (Myadestes obscurus) and Puaiohi (M. palmeri), were captive‐reared and re‐introduced into their historic range in Hawai`i by The Peregrine Fund, in collaboration with the U.S. Geological Survey–Biological Resources Division (BRD) and the Hawai`i State Department of Land and Natural Resources. This paper describes the management techniques that were developed (collection of wild eggs, artificial incubation, hand‐rearing, captive propagation, and release) with the non‐endangered surrogate species, the `Oma`o; techniques that are now being used for recovery of the endangered Puaiohi. In 1995 and 1996, 29 viable `Oma`o eggs were collected from the wild. Of 27 chicks hatched, 25 were hand‐reared and released into Pu`u Wa`awa`a Wildlife Reserve. Using the techniques developed for the `Oma`o, a captive propagation and release program was initiated in 1996 to aid the recovery of the endangered Puaiohi. Fifteen viable Puaiohi eggs were collected from the wild (1996–1997) to establish a captive breeding flock to produce birds for re‐introduction. These Puaiohi reproduced for the first time in captivity in 1998 (total Puaiohi chicks reared in captivity 1996–1998 = 41). In 1999, 14 captive‐bred Puaiohi were re‐introduced into the Alaka`i Swamp, Kaua`i. These captive‐bred birds reproduced and fledged seven chicks in the wild after release. This is the first endangered passerine recovery program using this broad spectrum of management techniques (collection of wild eggs, artificial incubation, hand‐rearing, captive‐breeding, and release) in which re‐introduced birds survived and bred in the wild. Long‐term population monitoring will be published separately [BRD, in preparation]. Zoo Biol 19:263–277, 2000. © 2000 Wiley‐Liss, Inc. 相似文献
999.
Erik J.B. Landin Christopher Williams Sara A. Ryan Alice Bochel Nahida Akter Christina Redfield Richard B. Sessions Neesha Dedi Richard J. Taylor Matthew P. Crump 《The Journal of biological chemistry》2021,297(6)
The α1-acid glycoprotein (AGP) is an abundant blood plasma protein with important immunomodulatory functions coupled to endogenous and exogenous ligand-binding properties. Its affinity for many drug-like structures, however, means AGP can have a significant effect on the pharmokinetics and pharmacodynamics of numerous small molecule therapeutics. Staurosporine, and its hydroxylated forms UCN-01 and UCN-02, are kinase inhibitors that have been investigated at length as antitumour compounds. Despite their potency, these compounds display poor pharmokinetics due to binding to both AGP variants, AGP1 and AGP2. The recent renewed interest in UCN-01 as a cytostatic protective agent prompted us to solve the structure of the AGP2–UCN-01 complex by X-ray crystallography, revealing for the first time the precise binding mode of UCN-01. The solution NMR suggests AGP2 undergoes a significant conformational change upon ligand binding, but also that it uses a common set of sidechains with which it captures key groups of UCN-01 and other small molecule ligands. We anticipate that this structure and the supporting NMR data will facilitate rational redesign of small molecules that could evade AGP and therefore improve tissue distribution. 相似文献
1000.
Tanner C. Dixon Christina M. Merrick Joni D. Wallis Richard B. Ivry Jose M. Carmena 《PLoS computational biology》2021,17(11)
Pronounced activity is observed in both hemispheres of the motor cortex during preparation and execution of unimanual movements. The organizational principles of bi-hemispheric signals and the functions they serve throughout motor planning remain unclear. Using an instructed-delay reaching task in monkeys, we identified two components in population responses spanning PMd and M1. A “dedicated” component, which segregated activity at the level of individual units, emerged in PMd during preparation. It was most prominent following movement when M1 became strongly engaged, and principally involved the contralateral hemisphere. In contrast to recent reports, these dedicated signals solely accounted for divergence of arm-specific neural subspaces. The other “distributed” component mixed signals for each arm within units, and the subspace containing it did not discriminate between arms at any stage. The statistics of the population response suggest two functional aspects of the cortical network: one that spans both hemispheres for supporting preparatory and ongoing processes, and another that is predominantly housed in the contralateral hemisphere and specifies unilateral output. 相似文献