首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   16244篇
  免费   1445篇
  国内免费   11篇
  2022年   104篇
  2021年   196篇
  2020年   131篇
  2019年   166篇
  2018年   219篇
  2017年   220篇
  2016年   323篇
  2015年   569篇
  2014年   552篇
  2013年   740篇
  2012年   976篇
  2011年   895篇
  2010年   676篇
  2009年   537篇
  2008年   829篇
  2007年   826篇
  2006年   732篇
  2005年   844篇
  2004年   713篇
  2003年   670篇
  2002年   665篇
  2001年   244篇
  2000年   198篇
  1999年   221篇
  1998年   229篇
  1997年   162篇
  1996年   183篇
  1995年   159篇
  1994年   138篇
  1993年   176篇
  1992年   169篇
  1991年   179篇
  1990年   160篇
  1989年   163篇
  1988年   168篇
  1987年   142篇
  1986年   136篇
  1985年   128篇
  1984年   123篇
  1983年   112篇
  1982年   119篇
  1981年   144篇
  1980年   123篇
  1979年   135篇
  1978年   122篇
  1977年   118篇
  1976年   102篇
  1974年   123篇
  1973年   133篇
  1972年   100篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
The Asian Tree Toad genus Pedostibes, as currently understood, exhibits a conspicuously disjunct distribution, posing several immediate questions relating to the biogeography and taxonomy of this poorly known group. The type species, P. tuberculosus and P. kempi, are known only from India, whereas P. hosii, P. rugosus, and P. everetti are restricted to Southeast Asia. Several studies have shown that these allopatric groups are polyphyletic, with the Indian Pedostibes embedded within a primarily South Asian clade of toads, containing the genera Adenomus, Xanthophryne, and Duttaphrynus. Southeast Asian Pedostibes on the other hand, are nested within a Southeast Asian clade, which is the sister lineage to the Southeast Asian river toad genus Phrynoidis. We demonstrate that Indian and Southeast Asian Pedostibes are not only allopatric and polyphyletic, but also exhibit significant differences in morphology and reproductive mode, indicating that the Southeast Asian species’ are not congeneric with the true Pedostibes of India. As a taxonomic solution, we describe a new genus, Rentapia gen. nov. to accommodate the Southeast Asian species.  相似文献   
4.
The distribution of grooming and touching behaviours was recorded in a group of captive ring-tailed lemurs. Grooming was found to be performed chiefly by older, higher ranking animals; touching (i.e., “reach out and touch” behaviour) was directed primarily by younger, low ranking animals to older, high ranking individuals. It is suggested that such touching is a submissive gesture in this species.  相似文献   
5.
Ffh is a component of a bacterial ribonucleoprotein complex homologous to the signal recognition particle (SRP) of eukaryotes. It comprises three domains that mediate both binding to the hydrophobic signal sequence of the nascent polypeptide and the GTP-dependent interaction of Ffh with a structurally homologous GTPase of the SRP receptor. The X-ray structures of the two-domain 'NG' GTPase of Ffh in complex with Mg2+GDP and GDP have been determined at 2.0 A resolution. The structures explain the low nucleotide affinity of Ffh and locate two regions of structural mobility at opposite sides of the nucleotide-binding site. One of these regions includes highly conserved sequence motifs that presumably contribute to the structural trigger signaling the GTP-bound state. The other includes the highly conserved interface between the N and G domains, and supports the hypothesis that the N domain regulates or signals the nucleotide occupancy of the G domain.  相似文献   
6.
7.
The coliform bacterial population in the Grand Forks, N.Dak. sewage system was examined for multiple-antibiotic-resistant organisms over a 1-year period. Multiple-antibiotic-resistant coliforms were found to be common in the sewage, and their numbers remained fairly constant relative to the total coliform population throughout the year. Resistance to kanamycin, tetracycline, and ampicillin was found to be transferable at variable rates. Transfer rates were found to be temperature sensitive and were optimal at 35 degrees C. Although 75% of the multiple-antibiotic-resistant coliforms were capable of transferring resistance at some level, only 25% were capable of transferring resistance at rates greater than 10(-3) transconjugants per initial donor.  相似文献   
8.
9.
The effect of the pentapeptide H-Cys-Tyr-Ile-Gln-Asn-OH to act like melanocyte-stimulating hormone-releasing factor (MSH-RF) was studied. This peptide decreases at ng amounts the MSH content of the rat pituitary and increases plasma MSH concentration. This agent also stimulates the release of MSH in animals with eminence lesion, indicating a direct action of the pentapeptide on the gland.  相似文献   
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号