全文获取类型
收费全文 | 9195篇 |
免费 | 702篇 |
国内免费 | 976篇 |
出版年
2024年 | 20篇 |
2023年 | 107篇 |
2022年 | 285篇 |
2021年 | 506篇 |
2020年 | 377篇 |
2019年 | 450篇 |
2018年 | 375篇 |
2017年 | 275篇 |
2016年 | 408篇 |
2015年 | 582篇 |
2014年 | 699篇 |
2013年 | 782篇 |
2012年 | 886篇 |
2011年 | 765篇 |
2010年 | 491篇 |
2009年 | 464篇 |
2008年 | 530篇 |
2007年 | 466篇 |
2006年 | 385篇 |
2005年 | 297篇 |
2004年 | 293篇 |
2003年 | 260篇 |
2002年 | 212篇 |
2001年 | 146篇 |
2000年 | 128篇 |
1999年 | 129篇 |
1998年 | 82篇 |
1997年 | 62篇 |
1996年 | 52篇 |
1995年 | 60篇 |
1994年 | 64篇 |
1993年 | 40篇 |
1992年 | 36篇 |
1991年 | 43篇 |
1990年 | 31篇 |
1989年 | 23篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 850 毫秒
971.
Arsenic trioxide induces gallbladder carcinoma cell apoptosis via downregulation of Bcl-2 总被引:7,自引:0,他引:7
Gallbladder carcinoma (GBC), an aggressive and mostly lethal malignancy, is known to be resistant to a number of apoptotic stimuli. Here, we report for the first time the pro-apoptosis role of arsenic trioxide (As2O3) in gallbladder carcinoma and identify the contribution of Bcl-2 in the As2O3-induced apoptosis. The treatment of As2O3 in gallbladder carcinoma cells could induce apoptosis in a dose-dependent manner and downregulate the expression of anti-apoptotic protein Bcl-2 at mRNA level. Moreover, Bcl-2 overexpression could protect gallbladder carcinoma cells from As2O3-induced apoptosis, indicating the contribution of Bcl-2 in As2O3-induced apoptosis. Taken together, these results suggest that arsenic trioxide induces gallbladder carcinoma cell apoptosis via downregulation of Bcl-2, which may have important therapeutic implications in gallbladder carcinoma patients. 相似文献
972.
973.
A new cell line from larval fat bodies of the bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae) 总被引:1,自引:0,他引:1
Zhang H Zhang YA Qin Q Wang Y Li X Miao L Yin Z Zhang A Qu L Ding C 《In vitro cellular & developmental biology. Animal》2006,42(10):290-293
Summary A new cell line, designated IOZCAS-Ha-I, was initiated from the fat body of larvae of Helicoverpa armigera (Lepidoptera: Noctuidae) in TNM-FH medium containing 10% fetal bovine serum. Spherical cells were predominant among the various
cell types. The cell line showed a typical lepidopteran chromosome pattern ranging from 58 to 239 chromosomes in the majority
of the cells, it was confirmed to have originated from the H. armigera by the DNA amplification-fingerprinting polymerase chain reaction (DAF-PCR) technique. The new cell line was only slightly
susceptible to the multiple nucleocapsid nuclear polyhedrosis viruses (NPV) from H. armigera. 相似文献
974.
Carotenoid biosynthesis in cyanobacteria: structural and evolutionary scenarios based on comparative genomics 下载免费PDF全文
Carotenoids are widely distributed pigments in nature and their biosynthetic pathway has been extensively studied in various organisms. The recent access to the overwhelming amount genomic data of cyanobacteria has given birth to a novel approach called comparative genomics. The putative enzymes involved in the carotenoid biosynthesis among the cyanobacteria were determined by similarity-based tools. The reconstruction of biosynthetic pathway was based on the related enzymes. It is interesting to find that nearly all the cyanobacteria share quite similar pathway to synthesize beta-carotene except for Gloeobacter violaceus PCC 7421. The enzymes, crtE-B-P-Qb-L, involved in the upstream pathway are more conserved than the subsequent ones (crtW-R). In addition, many carotenoid synthesis enzymes exhibit diversity in structure and function. Such examples in the families of zeta -carotene desaturase, lycopene cylases and carotene ketolases were described in this article. When we mapped these crt genes to the cyanobacterial genomes, the crt genes showed great structural variation among species. All of them are dispersed on the whole chromosome in contrast to the linear adjacent distribution of the crt gene cluster in other eubacteria. Moreover, in unicellular cyanobacteria, each step of the carotenogenic pathway is usually catalyzed by one gene product, whereas multiple ketolase genes are found in filamentous cyanobacteria. Such increased numbers of crt genes and their correlation to the ecological adaptation were carefully discussed. 相似文献
975.
Prediction of protein structural class with Rough Sets 总被引:1,自引:0,他引:1
Background
A new method for the prediction of protein structural classes is constructed based on Rough Sets algorithm, which is a rule-based data mining method. Amino acid compositions and 8 physicochemical properties data are used as conditional attributes for the construction of decision system. After reducing the decision system, decision rules are generated, which can be used to classify new objects. 相似文献976.
977.
Background
Francisella tularensis is a zoonotic intracellular bacterial pathogen that causes tularemia. The subspecies tularensis is highly virulent and is classified as a category A agent of biological warfare because of its low infectious dose by an aerosol route, and its ability to cause severe disease. In macrophages F. tularensis exhibits a rather novel intracellular lifestyle; after invasion it remains in a phagosome for three to six hours before escaping to, and replicating in the cytoplasm. The molecular mechanisms that allow F. tularensis to invade and replicate within a host cell have not been well defined. 相似文献978.
The anamorph determination of Cordyceps sinensis remains problematic due to the lack of clear links between the sexual and conidial forms of the fungus. In this study, we applied molecular approaches to analyze the genetic variation of Cordyceps sinensis and its allies to identify the anamorph-teleomorph connection. The sequences of the internal transcribed spacers (ITS1 and ITS2) and 5.8S ribosomal RNA gene of Cordyceps sinensis (teleomorph) collected from Qingzang plateau (altitude over 4000m), Tibet and several related asexual conidial forms were determined. The sequence comparison showed that Cordyceps sinensis was most closely related to Hirsutella sinensis, and was clearly divergent from Paecilomyces sinensis, Stachybotrys sp. or Tolypocladium sp.; distance values, estimated according to Kimura two-parameter models between Cordyceps sinensis and Hirsutella sinensis, were extremely low (<0.02), whereas distance values between Cordyceps sinensis and Paecilomyces sinensis, Stachybotrys sp. and Tolypocladium sp. were 0.34, 0.21 and 0.25, respectively. Taken together, Hirsutella sinensis and Cordyceps sinensis are the different stages of the life cycle stages of the same organism. Hirsutella sinensis is therefore the anamorph of Cordyceps sinensis, rather than Paecilomyces sinensis or other species. The possible reasons as to why different taxa can be obtained when culturing Cordyceps sinensis are also discussed. 相似文献
979.
甲醛对大鼠脑影响的实验形态学研究 总被引:5,自引:1,他引:5
24只Wistar大鼠,体重200~280g。6只为正常对照组,18只为实验性甲醛蒸气吸入组,每天定时吸入甲醛蒸气(200mg/m3)30分钟,分别在7、14和21天后处死,然后观察大脑皮层神经细胞的酶组织化学变化及超微结构变化。酶组织化学结果显示:SDH、Mg-MTase,ChE活性降低↓;ALP、ACP、MAO活性增强↑。超微结构变化可见(21天):皮层神经细胞线粒体嵴断裂、肿胀、空泡样变。表明甲醛对大脑皮层神经细胞的功能和结构均有影响。 相似文献
980.