全文获取类型
收费全文 | 12946篇 |
免费 | 700篇 |
国内免费 | 1065篇 |
出版年
2024年 | 36篇 |
2023年 | 270篇 |
2022年 | 348篇 |
2021年 | 459篇 |
2020年 | 412篇 |
2019年 | 380篇 |
2018年 | 398篇 |
2017年 | 310篇 |
2016年 | 373篇 |
2015年 | 563篇 |
2014年 | 629篇 |
2013年 | 729篇 |
2012年 | 448篇 |
2011年 | 485篇 |
2010年 | 473篇 |
2009年 | 601篇 |
2008年 | 596篇 |
2007年 | 595篇 |
2006年 | 606篇 |
2005年 | 591篇 |
2004年 | 539篇 |
2003年 | 433篇 |
2002年 | 492篇 |
2001年 | 323篇 |
2000年 | 292篇 |
1999年 | 288篇 |
1998年 | 257篇 |
1997年 | 257篇 |
1996年 | 240篇 |
1995年 | 238篇 |
1994年 | 254篇 |
1993年 | 226篇 |
1992年 | 205篇 |
1991年 | 159篇 |
1990年 | 139篇 |
1989年 | 130篇 |
1988年 | 129篇 |
1987年 | 95篇 |
1986年 | 101篇 |
1985年 | 92篇 |
1984年 | 115篇 |
1983年 | 65篇 |
1982年 | 77篇 |
1981年 | 55篇 |
1980年 | 57篇 |
1979年 | 52篇 |
1978年 | 29篇 |
1977年 | 21篇 |
1976年 | 21篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Joseph V. Rodricks 《人类与生态风险评估》2014,20(1):3-28
The publication in 1962 of Rachel Carson's Silent Spring marks the mid-point in a century that saw, in its first half, the emergence of public health concerns related to human exposures to chemicals, and, in its second half, the emergence of public policies to deal with those concerns. Those policies made it imperative that the scientific community come to grips with the problem of identifying exposure levels not likely to cause harm. This problem was not significantly discussed within the scientific community until the 1950s, and well-described methods for practical solutions to it did not appear until the 1970s. An important report from the National Academy of Sciences, published in 1983 (Risk Assessment in the Federal Government), provided an analysis of these emerging methods, and recommended a useful framework for the assessment and management of risk. This framework remains central to public health and regulatory decision-making. A high-level perspective is offered on events leading to and following the 1983 report. The article describes early thinking about chemical toxicity and the scientific path that thinking followed through the 20th century, and to the present. 相似文献
3.
4.
5.
Larvae and nymphs of the tick Ixodes ricinus L. display similar reactions to analogs of the insect juvenile hormones (methoprene and pyriproxyfen), which induce at both stages juvenalization of the Haller's sense organ regenerates. Similar effects were also described for retinoic acid. Unlike juvenoids, retinoic acid can affect not only regeneration, but also normal development of the Haller's organ and cause changes corresponding to so-called regenerative induction. Amputation of the leg and treatment with retinoic acid do not affect the duration of larval or nymphal development, while juvenoids somewhat accelerate their development. 相似文献
6.
Birds often lose feathers during predation attempts, and thisability has evolved as a means of escape. Because predatorsare more likely to grab feathers on the rump and the back thanon the ventral side of an escaping bird, we predicted that theformer feathers would have evolved to be relatively looselyattached as an antipredator strategy in species that frequentlydie from predation. We estimated the force required to removefeathers from the rump, back, and breast by pulling featherswith a spring balance from a range of European bird speciesin an attempt to investigate ecological factors associated withease of feather loss during predation attempts. The force requiredto loosen a feather from the rump was less than that requiredto loosen a feather from back, which in turn was less than thatrequired to loosen a feather from the breast. The relative forceneeded to loosen rump feathers compared with feathers from theback and the breast was smaller for prey species preferred bythe most common predator of small passerine birds, the sparrowhawkAccipiter nisus. Likewise, the relative force was also smallerin species with a high frequency of complete tail loss amongfree-living birds, which we used as an index of the frequencyof failed predation attempts. The relative force required toremove feathers from the rump was smaller in species with ahigh frequency of fear screams, another measure of the relativeimportance of predation as a cause of death. Feather loss requiredparticularly little force among solitarily breeding bird speciesthat suffer the highest degree of predation. Antipredator defensein terms of force required to remove feathers from the rumpwas larger in species with a strong antiparasite defense interms of T-cellmediated immune response. These findingsare consistent with the hypothesis that different defenses areantagonistic and that they are traded off against each other. 相似文献
7.
8.
Splenic gene expression profiling in White Leghorn layer inoculated with the Salmonella enterica serovar Enteritidis
下载免费PDF全文
![点击此处可从《Animal genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Salmonella enterica serovar Enteritidis (SE) is a foodborne pathogen that can threaten human health through contaminated poultry products. Live poultry, chicken eggs and meat are primary sources of human salmonellosis. To understand the genetic resistance of egg‐type chickens in response to SE inoculation, global gene expression in the spleen of 20‐week‐old White Leghorn was measured using the Agilent 4 × 44 K chicken microarray at 7 and 14 days following SE inoculation (dpi). Results showed that there were 1363 genes significantly differentially expressed between inoculated and non‐inoculated groups at 7 dpi (I7/N7), of which 682 were up‐regulated and 681 were down‐regulated genes. By contrast, 688 differentially expressed genes were observed at 14 dpi (I14/N14), of which 371 were up‐regulated genes and 317 were down‐regulated genes. There were 33 and 28 immune‐related genes significantly differentially expressed in the comparisons of I7/N7 and I14/N14 respectively. Functional annotation revealed that several Gene Ontology (GO) terms related to immunity were significantly enriched between the inoculated and non‐inoculated groups at 14 dpi but not at 7 dpi, despite a similar number of immune‐related genes identified between I7/N7 and I14/N14. The immune response to SE inoculation changes with different time points following SE inoculation. The complicated interaction between the immune system and metabolism contributes to the immune responses to SE inoculation of egg‐type chickens at 14 dpi at the onset of lay. GC, TNFSF8, CD86, CD274, BLB1 and BLB2 play important roles in response to SE inoculation. The results from this study will deepen the current understanding of the genetic response of the egg‐type chicken to SE inoculation at the onset of egg laying. 相似文献
9.
《DNA Repair》2017
Human PrimPol is a recently discovered bifunctional enzyme that displays DNA template-directed primase and polymerase activities. PrimPol has been implicated in nuclear and mitochondrial DNA replication fork progression and restart as well as DNA lesion bypass. Published evidence suggests that PrimPol is a Mn2+-dependent enzyme as it shows significantly improved primase and polymerase activities when binding Mn2+, rather than Mg2+, as a divalent metal ion cofactor. Consistently, our fluorescence anisotropy assays determined that PrimPol binds to a primer/template DNA substrate with affinities of 29 and 979 nM in the presence of Mn2+ and Mg2+, respectively. Our pre-steady-state kinetic analysis revealed that PrimPol incorporates correct dNTPs with 100-fold higher efficiency with Mn2+ than with Mg2+. Notably, the substitution fidelity of PrimPol in the presence of Mn2+ was determined to be in the range of 3.4 × 10−2 to 3.8 × 10−1, indicating that PrimPol is an error-prone polymerase. Furthermore, we kinetically determined the sugar selectivity of PrimPol to be 57–1800 with Mn2+ and 150–4500 with Mg2+, and found that PrimPol was able to incorporate the triphosphates of two anticancer drugs (cytarabine and gemcitabine), but not two antiviral drugs (emtricitabine and lamivudine). 相似文献
10.