全文获取类型
收费全文 | 65673篇 |
免费 | 4446篇 |
国内免费 | 2808篇 |
出版年
2023年 | 1062篇 |
2022年 | 1029篇 |
2021年 | 2088篇 |
2020年 | 2050篇 |
2019年 | 2778篇 |
2018年 | 2470篇 |
2017年 | 1638篇 |
2016年 | 1767篇 |
2015年 | 2208篇 |
2014年 | 3731篇 |
2013年 | 4847篇 |
2012年 | 2719篇 |
2011年 | 3554篇 |
2010年 | 2585篇 |
2009年 | 2941篇 |
2008年 | 3008篇 |
2007年 | 3131篇 |
2006年 | 2769篇 |
2005年 | 2561篇 |
2004年 | 2275篇 |
2003年 | 1961篇 |
2002年 | 1838篇 |
2001年 | 1432篇 |
2000年 | 1240篇 |
1999年 | 1199篇 |
1998年 | 1079篇 |
1997年 | 971篇 |
1996年 | 936篇 |
1995年 | 873篇 |
1994年 | 821篇 |
1993年 | 767篇 |
1992年 | 722篇 |
1991年 | 673篇 |
1990年 | 526篇 |
1989年 | 511篇 |
1988年 | 462篇 |
1987年 | 392篇 |
1986年 | 345篇 |
1985年 | 501篇 |
1984年 | 745篇 |
1983年 | 505篇 |
1982年 | 578篇 |
1981年 | 501篇 |
1980年 | 406篇 |
1979年 | 370篇 |
1978年 | 282篇 |
1977年 | 239篇 |
1976年 | 231篇 |
1974年 | 135篇 |
1973年 | 152篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
41.
《Developmental cell》2022,57(5):610-623.e8
42.
Phytochemical analysis of dried twigs of Marsdenia roylei (family Asclepiadaceae) has resulted in the isolation of a trisaccharide, maryal, and a diglycoside, rolinose. Their structures were determined as O-beta-D-oleandropyranosyl-(1-->4)-O-beta-D-digitoxopyranosyl++ +-(1-->4)-D- cymaral and ethyl O-beta-D-oleandropyranosyl-(1-->4)-O-3-O-methyl-6-deoxy-beta-D- allopyranoside, respectively, by chemical degradation and spectroscopic methods. 相似文献
43.
Masaru Kubota Ying-Wei Lin Keigo Hamahata Machiko Sawada Seiji Koishi Haruyo Hirota Yoshihiro Wakazono 《Mutation Research - Genetic Toxicology and Environmental Mutagenesis》2000,470(2):21
The occurrence of a second neoplasm is one of the major obstacles in cancer chemotherapy. The elucidation of the genotoxic effects induced by anti-cancer drugs is considered to be helpful in identifying the degree of cancer risk. Numerous investigations on cancer patients after chemotherapy have demonstrated: (i) an increase in the in vivo somatic cell mutant frequency (Mf) at three genetic loci, including hypoxanthine–guanine phosphoribosyl-transferase (hprt), glycophorin A (GPA), and the T-cell receptor (TCR), and (ii) alterations in the mutational spectra of hprt mutants. However, the time required for and the degree of such changes are quite variable among patients even if they have received the same chemotherapy, suggesting the existence of underlying genetic factor(s). Accordingly, some cancer patients prior to chemotherapy as well as patients with cancer-prone syndrome have been found to show an elevated Mf. Based on the information obtained from somatic cell mutation assays, an individualized chemotherapy should be considered in order to minimize the risk of a second neoplasm. 相似文献
44.
45.
Sven Skog Viola Eriksson Eva Eliasson 《Biochimica et Biophysica Acta (BBA)/General Subjects》1981,672(1):33-44
Suspension cultures of ‘Chang liver’ cells were synchronized by preincubation in a glutamine-deficient medium or by thymidine blockade. Specific arginase activity varied in the synchronized cultures, being high when the number of S-phase cells was maximal. A relationship between high arginase activity and a high percentage of (S+G2) cells was also found when unsynchronized cells were separated by velocity sedimentation. The increase in arginase activity near the G1/S border was totally inhibited in the presence of cycloheximide. The rate of decrease in activity after addition of the drug indicated that the variations in the rate of synthesis of the enzyme, while the rate of degradation was more or less constant, corresponding to 4–6% per h. The role of arginase in cells lacking a urea cycle and the regulation of arginase activity in ‘Chang liver’ cells is discussed. 相似文献
46.
47.
48.
《Cell calcium》2019
Alterations in the (bio)chemical and physical microenvironment of cells accompany and often promote disease formation and progression. This is particularly well established for solid cancers, which are typically stiffer than the healthy tissue in which they arise, and often display profound acidification of their interstitial fluid. Cell surface receptors can sense changes in the mechanical and (bio)chemical properties of the surrounding extracellular matrix and fluid, and signalling through these receptors is thought to play a key role in disease development and advancement. This review will look at ion channels and G protein coupled receptors that are activated by mechanical cues and extracellular acidosis, and stimulation of which results in increases in intracellular Ca2+ concentrations. Cellular Ca2+ levels are dysregulated in cancer as well as cancer-associated cells, and mechano- and proton-sensing proteins likely contribute to these aberrant intracellular Ca2+ signals, making them attractive targets for therapeutic intervention. 相似文献
49.
In the large arteries, it is believed that elastin provides the resistance to stretch at low pressure, while collagen provides the resistance to stretch at high pressure. It is also thought that elastin is responsible for the low energy loss observed with cyclic loading. These tenets are supported through experiments that alter component amounts through protease digestion, vessel remodeling, normal growth, or in different artery types. Genetic engineering provides the opportunity to revisit these tenets through the loss of expression of specific wall components. We used newborn mice lacking elastin (Eln−/−) or two key proteins (lysyl oxidase, Lox−/−, or fibulin-4, Fbln4−/−) that are necessary for the assembly of mechanically-functional elastic fibers to investigate the contributions of elastic fibers to large artery mechanics. We determined component content and organization and quantified the nonlinear and viscoelastic mechanical behavior of Eln−/−, Lox−/−, and Fbln4−/− ascending aorta and their respective controls. We confirmed that the lack of elastin, fibulin-4, or lysyl oxidase leads to absent or highly fragmented elastic fibers in the aortic wall and a 56–97% decrease in crosslinked elastin amounts. We found that the resistance to stretch at low pressure is decreased only in Eln−/− aorta, confirming the role of elastin in the nonlinear mechanical behavior of the aortic wall. Dissipated energy with cyclic loading and unloading is increased 53–387% in Eln−/−, Lox−/−, and Fbln4−/− aorta, indicating that not only elastin, but properly assembled and crosslinked elastic fibers, are necessary for low energy loss in the aorta. 相似文献
50.