全文获取类型
收费全文 | 9222篇 |
免费 | 671篇 |
国内免费 | 2篇 |
出版年
2024年 | 4篇 |
2023年 | 51篇 |
2022年 | 126篇 |
2021年 | 219篇 |
2020年 | 132篇 |
2019年 | 172篇 |
2018年 | 226篇 |
2017年 | 188篇 |
2016年 | 312篇 |
2015年 | 500篇 |
2014年 | 581篇 |
2013年 | 682篇 |
2012年 | 819篇 |
2011年 | 841篇 |
2010年 | 550篇 |
2009年 | 425篇 |
2008年 | 555篇 |
2007年 | 559篇 |
2006年 | 484篇 |
2005年 | 500篇 |
2004年 | 421篇 |
2003年 | 401篇 |
2002年 | 346篇 |
2001年 | 80篇 |
2000年 | 57篇 |
1999年 | 83篇 |
1998年 | 90篇 |
1997年 | 64篇 |
1996年 | 54篇 |
1995年 | 56篇 |
1994年 | 45篇 |
1993年 | 41篇 |
1992年 | 25篇 |
1991年 | 26篇 |
1990年 | 27篇 |
1989年 | 18篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 3篇 |
排序方式: 共有9895条查询结果,搜索用时 15 毫秒
71.
72.
Maurizio Meta Marco Ponte Marina Guastella Claudia Semino Gabriella Pietra Giovanni Battista Ratto Giovanni Melioli 《Cancer immunology, immunotherapy : CII》1995,40(4):235-240
Despite the combined use of surgery and chemoradiotherapy, the poor prognosis of advanced non-smallcell lung cancer (NSCLC) requires the definition of new therapeutic approaches. The presence of T lymphocytes, with peculiar phenotypic, functional and molecular characteristics within the tumour, suggested the possible use of these cells, expanded in vitro, in protocols of adoptive immunotherapy. We have described how a population of oligoclonal T lymphocytes, derived from advanced NSCLC, can be expanded in vitro and has the capability of lysing autologous cancer cells. What is more important, we observed that patients with advanced NSCLC, treated with TIL expanded in vitro and recombinant interleukin-2, seemed to have a disease-free period longer than that of patients treated with conventional chemoradiotherapy. in an attempt to find new sources of specific lymphocytes for immunotherapy, we describe the analysis of the phenotypic, functional and molecular characteristics of T lymphocytes, derived from lymph nodes draining advanced NSCLC. In this paper we show that these cells, have restriction patterns of T cell receptor chain similar to those detectable in the population of infiltrating T lymphocytes. This finding suggests that T cells derived from draining lymph nodes of advanced NSCLC have peculiar characteristics and can be a suitable source of effector cells for protocols of adoptive immunotherapy in lung cancer treatment. 相似文献
73.
The etioplast»chloroplast transition in the cotyledons of mustard seedlings (Sinapis alba L.) has been studied by electron microscopy. It was found that the active form of phytochrome, established by a red light pulse pretreatment, increases the initial rate and eliminates the lag of grana and stroma thylakoid formation after the onset of white light 60 h after sowing. The effect of a pretreatment with 15 s red light pulses is fully reversible by 756 nm light pulses. This reversibility is lost within 5 min. Evidence is presented which suggests that the time course of grana and stroma thylakoid formation is not correlated with the time course of the dispersal of the prolamellar body. The different functions of phytochrome and chlorophyll in controlling thylakoid formation are discussed. 相似文献
74.
Enhanced Rate of Expression and Biosynthesis of Neuropeptide Y After Kainic Acid-Induced Seizures 总被引:2,自引:0,他引:2
Romuald Bellmann Rudolf Widmann Claudia Olenik Dieter K. Meyer Dagmar Maas Josef Marksteiner Günther Sperk 《Journal of neurochemistry》1991,56(2):525-530
Recent studies have shown marked increases in brain content of neuropeptide Y (NPY) after seizures induced by intraperitoneal injection of kainic acid and after pentylenetetrazole kindling in the rat. We have now investigated possible changes in the rate of biosynthesis of NPY after kainic acid treatment, by using pulse-labeling of the peptide and by determining prepro-NPY mRNA concentrations. For pulse labeling experiments, [3H]tyrosine was injected into the frontal cortex, and the incorporation of the amino acid into NPY was determined after purifying the peptide by gel filtration chromatography, antibody affinity chromatography, and reversed-phase HPLC. At 2 and 30 days after kainic acid treatment, the rate of tyrosine incorporation was enhanced by approximately 380% in the cortex. In addition, concentrations of pre-pro-NPY mRNA were determined in four different brain areas by hybridization of Northern blots with a complementary 32P-labeled RNA probe 2, 10, 30, and 60 days after kainic acid treatment. Marked increases were observed in the frontal cortex (by up to 350% of controls), in the dorsal hippocampus (by 750%), and in the amygdala/pyriform cortex (by 280%) at all intervals investigated. In the striatum only a small, transient increase was observed. The data demonstrate increased expression of prepro-NPY mRNA and an enhanced rate of in vivo synthesis of NPY as a result of seizures induced by the neurotoxin kainic acid. 相似文献
75.
76.
Summary Two 4-hydroxybenzoate decarboxylase activities and a phenol carboxylase activity were found in cell-free extracts of a defined, 4-hydroxybenzoate- or phenol-grown consortium. Both decarboxylase activities were loosely membrane-associated and required K+ but a different pH and ion strength. Loss of activity of both decarboxylases by EDTA could be compensated by Zn2+ ions. The K
m values for 4-hydroxybenzoate and K+ of the decarboxylase activities with pH optima at 6.4 or 7.8 were 0.02 and 2.5 or 0.004 and 0.5 mm, respectively. 3,4-Dihydroxybenzoate, 3,4,5-tridydroxybenzoate, 3,5-dimethoxy-4-hydroxybenzoate and 3-chloro-4-hydroxybenzoate were also decarboxylated by both enzyme activities. The phenol carboxylase was a soluble enzyme with its pH optimum at 6.5. It required K+, Rb+ or NH
inf4
sup+
as monovalent, Zn2+, Mg2+, Mn2+ or Ni2+ as divalent cations and catalysed the carboxylation of phenol if 2,4-,2,3,4- or 2,4,6-hydroxybezoates were absent. The three enzyme activities were not influenced by Avidin and thus were probably not biotin-dependent enzymes.
Offprint requests to: J. Winter 相似文献
77.
In amphibians and teleosts, retina and tectum grow incongruently. In order to maintain the retinotopy of the retinotectal projection, Gaze, Keating, and Chung (1974) postulated a shifting of terminals throughout growth. In order to test the possibility that ingrowing retinal fibers are the driving force for this shifting, we induced a permanent retinal projection into the ipsilateral tectum in juveniles of the cichlid fish Haplochromis burtoni. The surface of the tectum had increased (11–18 months later) 2.5–5.8 times, and the surface of the retina 8.6–14 times. Filling of ganglion cells with horseradish peroxidase (HRP) retrogradely from the tectum showed ipsilaterally regenerating ganglion cells only in the center of the retina. The position of ganglion cells indicated that the ipsilateral projection derived only from axotomized and regenerating retinal ganglion cells but not from those newly born. Ipsilaterally projecting retinal fibers showed terminals only in the rostral half of the tectum. Comparison of area of terminations of ipsilaterally projecting ganglion cells at various times after the crush provided no evidence for expansion or a shift into caudal tectal areas throughout the period of growth. These findings are compatible with the idea that newly ingrowing fibers induce older terminals to move caudally. 相似文献
78.
Iliana Ferrero C. Rossi N. Marmiroli Claudia Donnini P. P. Puglisi 《Antonie van Leeuwenhoek》1981,47(4):311-323
Mitochondrial protein synthesis, primary (antimycin-sensitive) respiration and secondary (antimycin-insensitive, salicyl-hydroxamate-sensitive)
respiration, have been characterized in the dimorphic yeastEndomycopsis capsularis.
The inhibition by chloramphenicol (CAP) of the morphogenetic development from the yeast-like form to the mycelial structure
in this yeast could represent the intervention in the morphogenetic process of mitochondrial protein synthesis, since chloramphenicol
blocks in vivo and in vitro mitochondrial protein synthesis. In fact, other functions such as primary and secondary respiration,
do not seem to play a role in the morphogenetic development since their inhibition by antimycin A (AA) or by salicyl-hydroxamic
acid (SHAM) does not affect the process. In addition, mitochondrial protein synthesis has been shown to be uninhibited by
the two respiratory inhibitors. 相似文献
79.
80.
Phycobilisomes, isolated in 500 mM Sorensen's phosphate buffer pH 6.8 from the red alga, Porphyridium cruentum, were analyzed by selective dissociation at various phosphate concentrations. The results are consistent with a structural model consisting of an allophycocyanin core, surrounded by a hemispherical layer of R-phycocyanin, with phycoerythrin being on the periphery. Such a structure also allows maximum energy transfer.Intact phycobilisomes transfer excitation energy ultimately to a pigment with a fluorescence emission maximum at 675 nm. This pigment is presumed to be allophycocyanin in an aggregated state. Uncoupling of energy transfer among the pigments, and physical release of the phycobiliproteins from the phycobilisome follow a parallel time-course; phycoerythrin is released first, followed by R-phycocyanin, and then allophycocyanin. In 55 mM phosphate buffer, the times at which 50% of each phycobiliprotein has dissociated are: phycoerythrin 40 min, R-phycocyanin 75 min, and allophycocyanin 140 min.The proposed arrangement of phycobiliproteins within phycobilisomes is also consistent with the results from precipitation reactions with monospecific antisera on intact and dissociated phycobilisomes. Anti-phycoerythrin reacts almost immediately with intact phycobilisomes, but reactivity with anti-R-phycocyanin and anti-allophycocyanin is considerably delayed, suggesting that the antigens are not accessible until a loosening of the phycobilisome structure occurs. Reaction with anti-allophycocyanin is very slow in P. cruentum phycobilisomes, but is much more rapid in phycobilisomes of Nostoc sp. which contains 6–8 times more allophycocyanin. It is proposed that allophycocyanin is partially exposed on the base of isolated intact phycobilisomes of both algae, but that in P. cruentum there are too few accessible sites to permit a rapid formation of a precipitate with anti-allophyocyanin.Phycobilisome dissociation is inversely proportional to phosphate concentration (500 mM to 2 mM), and is essentially unaffected by protein concentration in the range used (30–200 μg/ml). Phycobiliprotein release occurs in the same order (phycoerythrin > R-phycocyanin > allophycocyanin) in the pH range 5.4–8.0. 相似文献