全文获取类型
收费全文 | 8647篇 |
免费 | 993篇 |
国内免费 | 1942篇 |
出版年
2024年 | 46篇 |
2023年 | 176篇 |
2022年 | 334篇 |
2021年 | 548篇 |
2020年 | 425篇 |
2019年 | 507篇 |
2018年 | 421篇 |
2017年 | 377篇 |
2016年 | 476篇 |
2015年 | 640篇 |
2014年 | 769篇 |
2013年 | 742篇 |
2012年 | 845篇 |
2011年 | 733篇 |
2010年 | 517篇 |
2009年 | 469篇 |
2008年 | 474篇 |
2007年 | 391篇 |
2006年 | 358篇 |
2005年 | 333篇 |
2004年 | 286篇 |
2003年 | 258篇 |
2002年 | 256篇 |
2001年 | 167篇 |
2000年 | 127篇 |
1999年 | 113篇 |
1998年 | 65篇 |
1997年 | 52篇 |
1996年 | 33篇 |
1995年 | 38篇 |
1994年 | 40篇 |
1993年 | 36篇 |
1992年 | 70篇 |
1991年 | 53篇 |
1990年 | 49篇 |
1989年 | 51篇 |
1988年 | 30篇 |
1987年 | 34篇 |
1986年 | 29篇 |
1985年 | 32篇 |
1984年 | 26篇 |
1983年 | 19篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 14篇 |
1977年 | 9篇 |
1972年 | 11篇 |
1971年 | 9篇 |
1970年 | 9篇 |
1969年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Xu XB Pang JJ Cao JM Ni C Xu RK Peng XZ Yu XX Guo S Chen MC Chen C 《American journal of physiology. Heart and circulatory physiology》2005,289(4):H1643-H1651
Growth hormone (GH)-releasing peptides (GHRP), a class of synthetic peptidyl GH secretagogues, have been reported to exert a cardioprotective effect on cardiac ischemia. However, whether GHRP have a beneficial effect on chronic heart failure (CHF) is unclear, and the present work aims to clarify this issue. At 9 wk after pressure-overload CHF was created by abdominal aortic banding in rats, one of four variants of GHRP (GHRP-1, -2, and -6 and hexarelin, 100 mug/kg) or saline was injected subcutaneously twice a day for 3 wk. Echocardiography and cardiac catheterization were performed to monitor cardiac function and obtain blood samples for hormone assay. GHRP treatment significantly improved left ventricular (LV) function and remodeling in CHF rats, as indicated by increased LV ejection fraction, LV end-systolic pressure, and diastolic posterior wall thickness and decreased LV end-diastolic pressure and LV end-diastolic dimension. GHRP also significantly alleviated development of cardiac cachexia, as shown by increases in body weight and tibial length in CHF rats. Plasma CA, renin, ANG II, aldosterone, endothelin-1, and atrial natriuretic peptide were significantly elevated in CHF rats but were significantly decreased in GHRP-treated CHF rats. GHRP suppressed cardiomyocyte apoptosis and increased cardiac GH secretagogue receptor mRNA expression in CHF rats. GHRP also decreased myocardial creatine kinase release in hypophysectomized rats subjected to acute myocardial ischemia. We conclude that chronic administration of GHRP alleviates LV dysfunction, pathological remodeling, and cardiac cachexia in CHF rats, at least in part by suppressing stress-induced neurohormonal activations and cardiomyocyte apoptosis. 相似文献
992.
Chia SM Lin PC Quek CH Yin C Mao HQ Leong KW Xu X Goh CH Ng ML Yu H 《Journal of biotechnology》2005,118(4):434-447
Tissue engineering involves ex vivo seeding of anchorage-dependent mammalian cells onto scaffolds, or transplanting cells in vivo. The cell expansion currently requires repeated cell detachment from solid substrata by enzymatic, chemical or mechanical means. The report here presents a high yield three-dimensional culture and harvest system circumventing the conventional detachment requirements. Cells mixed with dilute cationic collagen were microencapsulated within an ultra-thin shell of synthetic polymers. The cationic collagen could rapidly form a conformal layer of collagen fibers around cells to support cell proliferation and functions. The collagen could be readily removed from cells with a buffer rinse after harvesting from the fragile microcapsules. The cells harvested from this system demonstrate improved attachment, morphology and functions over conventionally cultured cells, upon binding to ligand-conjugated polymer surfaces. The harvested cells can be re-encapsulated and allowed to proliferate again, or used immediately in applications. 相似文献
993.
Structure of the Dengue virus helicase/nucleoside triphosphatase catalytic domain at a resolution of 2.4 A
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Xu T Sampath A Chao A Wen D Nanao M Chene P Vasudevan SG Lescar J 《Journal of virology》2005,79(16):10278-10288
Dengue fever is an important emerging public health concern, with several million viral infections occurring annually, for which no effective therapy currently exists. The NS3 protein from Dengue virus is a multifunctional protein of 69 kDa, endowed with protease, helicase, and nucleoside 5'-triphosphatase (NTPase) activities. Thus, NS3 plays an important role in viral replication and represents a very interesting target for the development of specific antiviral inhibitors. We present the structure of an enzymatically active fragment of the Dengue virus NTPase/helicase catalytic domain to 2.4 A resolution. The structure is composed of three domains, displays an asymmetric distribution of charges on its surface, and contains a tunnel large enough to accommodate single-stranded RNA. Its C-terminal domain adopts a new fold compared to the NS3 helicase of hepatitis C virus, which has interesting implications for the evolution of the Flaviviridae replication complex. A bound sulfate ion reveals residues involved in the metal-dependent NTPase catalytic mechanism. Comparison with the NS3 hepatitis C virus helicase complexed to single-stranded DNA would place the 3' single-stranded tail of a nucleic acid duplex in the tunnel that runs across the basic face of the protein. A possible model for the unwinding mechanism is proposed. 相似文献
994.
Ji Q Lu J Chao Q Gu M Xu M 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2005,111(8):1495-1503
Wide-compatibility (WC) is one of the most important traits in rice, which can overcome the fertility barrier in the indica/japonica hybrids, and hence to make it possible to utilize the higher yield potential of inter-subspecific hybrids. The S
5
n
gene located on chromosome 6 has been previously reported to be responsible for the wide-compatibility in rice. Here we report
the precise location of the S
5
n
gene. In the first-pass mapping, the S
5
n
gene was restricted within a 200 kb region by using a population of 242 isogenic lines in combination with high-density markers
developed in the S
5 region. In the fine mapping, the S
5 region was further saturated with newly developed markers and more isogenic lines (549 in total) were investigated. Eventually,
the S
5
n
gene was mapped within a 50 kb region delimited by the left marker J13 and the right marker J17. One BAC clone screened from
the BAC library of the WC rice variety 02428 covered the whole S
5 region. Sequence analysis of the 50 kb region revealed two candidate genes, coding an aspartyl protease and a hypothetical
protein. This result would greatly accelerate both cloning and marker-assisted selection of this important S
5
n
gene.
Qing Ji and Jufei Lu have contributed equally to this paper. 相似文献
995.
Hong F Zhou J Liu C Yang F Wu C Zheng L Yang P 《Biological trace element research》2005,105(1-3):269-279
The effects of nano-TiO2 (rutile) on the photochemical reaction of chloroplasts of spinach were studied. The results showed that when spinach was
treated with 0.25% nano-TiO2, the Hill reaction, such as the reduction rate of FeCy, and the rate of evolution oxygen of chloroplasts was accelerated
and noncyclic photophosphorylation (nc-PSP) activity of chloroplasts was higher than cyclic photophosphorylation (c-PSP) activity,
the chloroplast coupling was improved and activities of Mg2+-ATPase and chloroplast coupling factor I (CF1)-ATPase on the thylakoid membranes were obviously activated. It suggested that photosynthesis promoted by nano-TiO2 might be related to activation of photochemical reaction of chloroplasts of spinach. 相似文献
996.
Profound difference of metabolic pharmacokinetics between pure glycyrrhizin and glycyrrhizin in licorice decoction 总被引:3,自引:0,他引:3
To investigate the difference of metabolic pharmacokinetics between pure glycyrrhizin (GZ) and GZ in licorice decoction, six New Zealand White rabbits were orally given pure GZ and licorice decoction containing equivalent content of GZ in a randomized crossover design. HPLC methods were used for the quantitation of GZ and glycyrrhetic acid (GA) in serum. The results indicated that the areas under curves (AUCs) of GZ and GA after administration of licorice decoction were significantly higher than those after pure GZ. This result was contradictory with that obtained in rats. To explore the mechanism of the pharmacokinetic difference, feces of rabbits, rats, pigs and humans were used to investigate the presystemic metabolism of pure GZ and GZ in licorice decoction. The results indicated that pure GZ was hydrolyzed to GA more rapidly and to a greater extent than that in licorice decoction by various feces. In addition, when pure GZ was fermented, the metabolic profiles of GA and 3-dehydroGA in rabbit feces were quite different from other feces. In conclusion, the bioavailabilities of GZ and GA are significantly better from licorice than from pure GZ in rabbits but the presystemic metabolism of pure GZ in rabbit is rather different from that in rat, pig and human. 相似文献
997.
Kinetic difference of berberine between hippocampus and plasma in rat after intravenous administration of Coptidis rhizoma extract 总被引:5,自引:0,他引:5
In order to investigate the pharmacokinetics of berberine in Coptidis rhizoma extract in rat hippocampus and plasma, a simple and accurate high-performance liquid chromatography method was employed in this study. Berberine was determined using a Hypersil C(18) column with an isocratic mobile phase of acetonitrile-0.05 M potassium dihydrogen phosphate (containing 0.5% triethylamine, pH 3.0) and with UV detection at 236 nm. The lower limit of quantification for berberine in both hippocampus and plasma was 24 ng/ml, and the lowest concentrations of berberine determined in rat hippocampus and plasma samples were 30.7 ng/ml at 48 h and 38.5 ng/ml at 4 h, respectively. The calibration curve for berberine was linear over the concentration range 24--6000 ng/ml. At this concentration range, the overall recoveries (90.6--94.2%) for berberine were determined and the accuracy of intra- and inter-day assays from rat samples were less than 7% RSD. Following intravenous administration of C. rhizoma extract at a dose of 10.2 mg/kg containing 3 mg/kg berberine, berberine in the plasma eliminated rapidly (t(1/2 beta)=1.13 h). However, berberine in the hippocampus increased rapidly (t(1/2 alpha)=0.215 h), peaked at 3.67 h with a concentration of 272 ng/g, and had a slow elimination rate (t(1/2 beta)=12.0 h), which suggests that berberine could have a direct action on neuron and accumulate in the hippocampus. This study first showed the pharmacokinetic characteristics of berberine in rat hippocampus and the kinetic characteristics of berberine are dissimilar in the hippocampus and plasma. 相似文献
998.
Shuangxia?Jin Xianlong?ZhangEmail author Shaoguang?liang Yichun?Nie Xiaoping?Guo Chao?Huang 《Plant Cell, Tissue and Organ Culture》2005,81(2):229-237
A reliable and high-efficiency system of transforming embryogenic callus (EC) mediated by Agrobacterium tumefaciens was developed in cotton. Various aspects of transformation were examined in efforts to improve the efficiency of producing transformants. LBA4404 and C58C3, harboring the pgusBin19 plasmid containing neomycin phosphortransferase II (npt-II) gene as a selection marker, were used for transformation. The effects of Agrobacterium strains, acetosyringone (AS), co-cultivation temperature, co-cultivation duration, Agrobacterium concentration and physiological status of EC on transformation efficiency were evaluated. Strain LBA4404 proved significantly better than C58C3. Agrobacterium at a concentration of 0.5 × 108 cells ml–1 (OD600=0.5) improved the efficiency of transformation. Relatively low co-cultivation temperature (19 °C) and short co-cultivation duration (48 h) were optimal for developing a highly efficient method of transforming EC. Concentration of AS at 50 mg l–1 during co-cultivation significantly increased transformation efficiency. EC growing 15 days after subculture was the best physiological status for transformation. An overall scheme for producing transgenic cotton is presented, through which an average transformation rate of 15% was obtained. 相似文献
999.
Salt-responsive genes in rice revealed by cDNA microarray analysis 总被引:19,自引:0,他引:19
1000.
INTRODUCTIONCytokinesis is a very complicated and carefully orches-trated process. During the last step of this process, anintercellular bridge is formed between the two daughtercells. A number of studies suggest that this intercellularbridge is not merel… 相似文献