全文获取类型
收费全文 | 19221篇 |
免费 | 1908篇 |
国内免费 | 4篇 |
出版年
2021年 | 258篇 |
2020年 | 182篇 |
2019年 | 248篇 |
2018年 | 257篇 |
2017年 | 248篇 |
2016年 | 425篇 |
2015年 | 621篇 |
2014年 | 747篇 |
2013年 | 947篇 |
2012年 | 1151篇 |
2011年 | 1150篇 |
2010年 | 696篇 |
2009年 | 715篇 |
2008年 | 955篇 |
2007年 | 987篇 |
2006年 | 942篇 |
2005年 | 873篇 |
2004年 | 853篇 |
2003年 | 820篇 |
2002年 | 776篇 |
2001年 | 363篇 |
2000年 | 331篇 |
1999年 | 330篇 |
1998年 | 225篇 |
1997年 | 221篇 |
1996年 | 214篇 |
1995年 | 214篇 |
1994年 | 182篇 |
1993年 | 200篇 |
1992年 | 277篇 |
1991年 | 263篇 |
1990年 | 236篇 |
1989年 | 224篇 |
1988年 | 215篇 |
1987年 | 212篇 |
1986年 | 204篇 |
1985年 | 229篇 |
1984年 | 227篇 |
1983年 | 175篇 |
1982年 | 209篇 |
1981年 | 147篇 |
1980年 | 146篇 |
1979年 | 166篇 |
1978年 | 150篇 |
1977年 | 126篇 |
1976年 | 126篇 |
1975年 | 114篇 |
1974年 | 150篇 |
1973年 | 130篇 |
1972年 | 104篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Protein metal-binding sites. 总被引:2,自引:0,他引:2
Metal ions have a role in a variety of important functions in proteins including protein folding, assembly, stability, conformational change, and catalysis. The presence or absence of a given metal ion is crucial to the conformation or activity of over one third of all proteins. Recent developments have been made in the understanding and design of metal-binding sites in proteins, an important and rapidly advancing area of protein engineering. 相似文献
2.
3.
4.
5.
6.
Internode length in Pisum. I. The effect of the Le/le gene difference on endogenous gibberellin-like substances 总被引:2,自引:0,他引:2
The allelopathic potential of the dry fruits of Washingtonia filifera (L. Linden) H. Wendl. was investigated. Leachates from fruits inhibited the germination of lettuce, wheat, red cabbage and cucumber seeds. The inhibitory effect was partly neutralized by kinetin (20 mg 1−1 ) and gibberellic acid (50 mg 1−1 ). The effect of kinetin was more pronounced at 25°C than at 20°C. Substances inhibiting germination were localized in the pericarp of the fruit and were resistant to high temperature. 相似文献
7.
Myoglobin (Mb) is the classic vertebrate oxygen-binding protein present in aerobic striated muscles. It functions principally in oxygen delivery and provides muscle with its characteristic red colour. Members of the Antarctic icefish family (Channichthyidae) are widely thought to be extraordinary for lacking cardiac Mb expression, a fact that has been attributed to their low metabolic rate and unusual evolutionary history. Here, we report that cardiac Mb deficit, associated with pale heart colour, has evolved repeatedly during teleost evolution. This trait affects both gill- and air-breathing species from temperate to tropical habitats across a full range of salinities. Cardiac Mb deficit results from total pseudogenization in three-spined stickleback and is associated with a massive reduction in mRNA level in two species that evidently retain functional Mb. The results suggest that near or complete absence of Mb-assisted oxygen delivery to heart muscle is a common facet of teleost biodiversity, even affecting lineages with notable oxygen demands. We suggest that Mb deficit may affect how different teleost species deal with increased tissue oxygen demands arising under climate change. 相似文献
8.
D Roberts 《Acta anatomica》1978,101(2):160-169
Retention of a retromandibular space has necessitated developing a system of mandibular protrusion in hominid species. It is possible that mandibular protrusion can be effected by a single muscle-the lateral pterygoid-and the motion controlled by the excentrically placed mandibular suspensory ligaments. The elasticity of the ligaments produces an integrity maintenance force between the articular condyle and eminence which is normally of minimal size. Excessive craniofacial flexion, or the retention of a juvenile configuration of the mandible, could result in increasing this integrity maintenance force and cause crepitation and clicking. Ajustment of the ligaments could reduce these pathological manifestations. 相似文献
9.
Ian H. Frasher Timothy Coolbear Sailen Mookerjea 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,799(2):102-105
Induction of inflammation by turpentine injection caused 1.5–2-fold increase of both sialy- and galactosyltransferase activity in liver homogenates. The effect was apparent after 12 h turpentine treatment. Serum sialytransferase activity started to increase in the inflamed rats after 18 h, reaching a maximum of 4-fold at 48 h. In contrast, galactosyltransferase activity in serum showed no significant increase. The coordinated and temporal increase of sialytransferase activity in liver and serum suggest involvement of a specific mechanism for the preferential release of this enzyme into serum. 相似文献
10.
C F Roberts 《Biochimica et biophysica acta》1970,201(2):267-283