全文获取类型
收费全文 | 6005篇 |
免费 | 843篇 |
国内免费 | 3篇 |
出版年
2021年 | 78篇 |
2019年 | 55篇 |
2016年 | 84篇 |
2015年 | 129篇 |
2014年 | 167篇 |
2013年 | 218篇 |
2012年 | 272篇 |
2011年 | 271篇 |
2010年 | 152篇 |
2009年 | 157篇 |
2008年 | 226篇 |
2007年 | 203篇 |
2006年 | 217篇 |
2005年 | 198篇 |
2004年 | 214篇 |
2003年 | 164篇 |
2002年 | 195篇 |
2001年 | 176篇 |
2000年 | 190篇 |
1999年 | 176篇 |
1998年 | 107篇 |
1997年 | 59篇 |
1996年 | 78篇 |
1995年 | 90篇 |
1994年 | 78篇 |
1993年 | 76篇 |
1992年 | 146篇 |
1991年 | 148篇 |
1990年 | 126篇 |
1989年 | 144篇 |
1988年 | 136篇 |
1987年 | 121篇 |
1986年 | 108篇 |
1985年 | 95篇 |
1984年 | 88篇 |
1983年 | 89篇 |
1982年 | 61篇 |
1981年 | 69篇 |
1980年 | 56篇 |
1979年 | 99篇 |
1978年 | 69篇 |
1977年 | 78篇 |
1976年 | 69篇 |
1975年 | 78篇 |
1974年 | 94篇 |
1973年 | 74篇 |
1972年 | 78篇 |
1971年 | 67篇 |
1970年 | 66篇 |
1968年 | 54篇 |
排序方式: 共有6851条查询结果,搜索用时 15 毫秒
1.
Demonstration that a chemically synthesized BPV1 oncoprotein and its C-terminal domain function to induce cellular DNA synthesis 总被引:17,自引:0,他引:17
Bovine papillomavirus type 1 contains the smallest known oncogene (ORF E5), encoding a hydrophobic 44 amino acid protein. To study the biochemical functions of the E5 oncoprotein, we have chemically synthesized it and several deletion mutant peptides. We demonstrate induction of cellular DNA synthesis in growth-arrested cells by microinjection of E5 oncoprotein. This activity can be broken down into two functionally distinguishable domains. Remarkably, the first domain, which alone is sufficient to induce cellular DNA synthesis, contains only the C-terminal 13 amino acids. This is the smallest known protein fragment that can autonomously activate cellular DNA synthesis. The second domain is the hydrophobic middle region, which by itself fails to induce cellular DNA synthesis but confers a 1000-fold increase in specific activity. The N-terminal one-third of the molecule is dispensable for induction of DNA synthesis. 相似文献
2.
3.
4.
5.
A method is described for the subcellular fractionation of goldfish xanthophores. The procedure produces relatively pure fractions of caroteniod droplets, pterinosomes, cytosol and what appears to be plasma membrane. The presence of a distinct pattern of proteins is shown to be associated with the carotenoid droplets. Treatment of the xanthophores with ACTH affects the buoyant density of some carotenoid droplets and stimulates the phosphorylation of a polypeptide associated with the carotenoid droplets. 相似文献
6.
Jeff A Johnson Heather RL Lerner Pamela C Rasmussen David P Mindell 《BMC evolutionary biology》2006,6(1):65-12
Background
Populations of the Oriental White-backed Vulture (Gyps bengalensis) have declined by over 95% within the past decade. This decline is largely due to incidental consumption of the non-steroidal anti-inflammatory veterinary pharmaceutical diclofenac, commonly used to treat domestic livestock. The conservation status of other Gyps vultures in southern Asia is also of immediate concern, given the lack of knowledge regarding status of their populations and the continuing existence of taxonomic uncertainties. In this study, we assess phylogenetic relationships for all recognized species and the majority of subspecies within the genus Gyps. The continuing veterinary use of diclofenac is an unknown but potential risk to related species with similar feeding habits to Gyps bengalensis. Therefore, an accurate assessment of the phylogenetic relationships among Gyps vultures should aid in their conservation by clarifying taxonomic uncertainties, and enabling inference of their respective relatedness to susceptible G. bengalensis. 相似文献7.
8.
9.
We conducted an experiment in a northern mixed-grass prairie at Wind Cave National Park, South Dakota, USA to evaluate the effect of defoliation frequency on aboveground net primary production (ANPP), shoot nitrogen concentration, and aboveground N yield of graminoids. ANPP was significantly reduced at weekly and biweekly defoliation frequencies, but unaffected relative to unclipped controls at monthly and bimonthly frequencies. By contrast, clipping at all frequencies increased shoot N concentration above that of controls, and this increase was greatest at monthly or more frequent defoliations. Total aboveground N yield and potential N yield to grazers were greatest at intermediate (bimonthly to biweekly) frequencies. We suggest that grazers may maximize their nutritional status in this system by periodically regrazing areas at frequencies near the approximately monthly optimum that we observed. 相似文献
10.