全文获取类型
收费全文 | 129974篇 |
免费 | 3263篇 |
国内免费 | 3668篇 |
专业分类
136905篇 |
出版年
2024年 | 99篇 |
2023年 | 518篇 |
2022年 | 1181篇 |
2021年 | 2155篇 |
2020年 | 1364篇 |
2019年 | 1723篇 |
2018年 | 13152篇 |
2017年 | 11524篇 |
2016年 | 8852篇 |
2015年 | 2972篇 |
2014年 | 3111篇 |
2013年 | 3361篇 |
2012年 | 7658篇 |
2011年 | 15644篇 |
2010年 | 13709篇 |
2009年 | 9671篇 |
2008年 | 11584篇 |
2007年 | 12926篇 |
2006年 | 1834篇 |
2005年 | 1776篇 |
2004年 | 2003篇 |
2003年 | 1920篇 |
2002年 | 1532篇 |
2001年 | 919篇 |
2000年 | 748篇 |
1999年 | 655篇 |
1998年 | 359篇 |
1997年 | 386篇 |
1996年 | 356篇 |
1995年 | 318篇 |
1994年 | 341篇 |
1993年 | 293篇 |
1992年 | 331篇 |
1991年 | 279篇 |
1990年 | 220篇 |
1989年 | 196篇 |
1988年 | 145篇 |
1987年 | 114篇 |
1986年 | 92篇 |
1985年 | 86篇 |
1984年 | 66篇 |
1983年 | 70篇 |
1982年 | 36篇 |
1979年 | 11篇 |
1972年 | 246篇 |
1971年 | 274篇 |
1965年 | 14篇 |
1962年 | 24篇 |
1944年 | 12篇 |
1940年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
951.
用RDA技术寻找肝再生相关基因的初步研究 总被引:2,自引:0,他引:2
利用表达性差异显示分析 (RDA)技术 ,研究大鼠 2 /3肝部分切除后 1h肝组织中基因的选择性表达 ,建立了大鼠 2 /3肝部分切除术后 1h再生肝组织选择性表达基因EST库。该库约含 3× 10 4 个独立克隆 ,其中 95 %以上的克隆含有插入片段 ,长度约 2 0 0~ 70 0bp不等 ,对随机挑出的 5 2个克隆的序列分析表明其中大多数基因与肝再生调控相关 (38/5 2 )。 10株未报道序列经RNA杂交证实 ,其中 6株与肝再生相关。 相似文献
952.
David R. ColemanIV Kumaralal Kaluarachchi Zhiyong Ren Xiaomin Chen John S. McMurray 《International journal of peptide research and therapeutics》2008,14(1):1-9
To answer the question of whether the conformation of the Leu-Pro bond is cis or trans in Ac-pTyr-Leu-Pro-Gln-Thr-Val-NH2 when complexed with the SH2 domain of Stat3, we substituted 2,2-dimethyloxazolidines derived from serine (Ser(ΨMe,Mepro)) and threonine (Thr(ΨMe,Mepro)) for proline. The 2,2-dimethyloxazolidine and 2,2-dimethylthiazolidine pseudoproline (ΨPro) analogs induce predominantly
cis Xxx-ΨPro peptide bonds. As these ΨPro analogs are acid-labile, the phosphopeptides were synthesized using Fmoc-based SPPS
using unprotected phosphotyrosine and 4-hydroxybenzoate as the linker that allowed release from the support by alkaline ammonolysis,
conditions that kept the oxazolidine rings intact. Incorporation of Ser(ΨMe,Mepro) resulted in 69% cis Leu-ΨPro bond content in aqueous solution whereas that for Thr(ΨMe,Mepro) analog was 63%. Affinities for Stat3 were 3–5 fold lower than the lead compound and were inversely correlated with cis content. Thus we conclude that the Leu-Pro peptide bond is trans when the peptide is bound to Stat3. 相似文献
953.
954.
Daniel R. Papaj Stephen L. Buchmann Avery L. Russell 《Arthropod-Plant Interactions》2017,11(3):307-315
Heteranthery is thought to reflect a division of labor, with some anthers serving a pollinator-feeding function and others serving a pollinating function. Mutualism theory predicts that each participant should try to maximize the benefit it receives from its partner: plants should allocate more pollen to pollination, and pollinators should collect more pollen. Accordingly, plant and pollinator may engage in a ‘tug of war’ with respect to pollen from each anther type, resulting in incomplete division of labor. Here, we explored this idea by conducting a fully factorial manipulation of the availability of pollen in long and short anthers of staminate flowers of Solanum houstonii. We found the following: (1) Bumble bees (Bombus impatiens) preferred to sonicate (collect pollen from) short anthers over long anthers, consistent with a role as feeding and pollinating anthers, respectively; (2) Blocking short anther pores alone increased sonication of long anthers and resulted in collection of pollen from long anthers; (3) Blocking long anther pores alone did not influence sonication of short anthers; (4) The increase in sonication of long anthers, when short anther pores are blocked, was greater when pollen was available in long anthers; (5) Despite shifting sonication effort to long anthers, bees do not move their bodies closer to long anther pores where pollen could be collected more effectively; and (6) analysis of the growth of corbicular loads over time spent buzzing indicates that significant amounts of pollen are collected from long anthers as well as short anthers. We conclude that bees can flexibly increase pollen collection from pollinating anthers, but are constrained from fully exploiting this pollen. This results in checks and balances between plant and bee that may help maintain heteranthery. 相似文献
955.
本文采用间接免疫荧光法(IF),RPHA法,ELISA法及斑点杂交技术检测10例无症状HB-sAg携带者及89例乙肝病人尿细胞中的HBsAg、HBeAg及HBVDNA,发现尿细胞中有HBsAg、HBeAg、HBVDNA存在。结果提示:乙肝无症状携带者及乙肝病人尿细胞中具有HBsAg、HBeAg、HBVDNA,因此更进一步证实尿液具有传染性。 相似文献
956.
To investigate the effect of human pyruvate carboxylase (hPC) on lactate formation in Chinese hamster ovary (CHO) cell lines,
FLAG-tagged hPC was introduced into a dihydrofolate-deficient CHO cell line (DG44). Three clones expressing high levels of
hPC, determined by Western blotting using an anti-FLAG monoclonal antibody, and a control cell line were established. Immunocytochemistry
revealed that a substantial amount of expressed hPC protein was localized in the mitochondria of the cells. hPC expression
did not impair cell proliferation. Rather, it improved cell viability at the end of adherent batch cultures with the serum-containing
medium probably because of reduced lactate formation. Compared with control cells, specific lactate production rate of the
three clones was decreased by 21–39%, which was because of a decreased specific glucose uptake rate and yield of lactate from
glucose. Reduced lactate formation by hPC expression was also observed in suspension fed-batch cultures using a serum-free
medium. Taken together, these results demonstrate that through the expression of the hPC enzyme, lactate formation in CHO
cell culture can be efficiently reduced. 相似文献
957.
采用聚合酶链式反应技术,扩增了水稻矮缩病毒(RDV)基因组第10号片段的编码序列,该片段编码病毒的非结构蛋白。对扩增产物进行了克隆和限制性内切酶分析,并绘制了物理图谱。克隆片段大小为1150 bp,含Sac I、Hind III、Nde I、BamH I、Sai I 等酶切位点,引物设计时还在该片段两侧增加了Bgl II和 EcoR I 切点,以便克隆到植物中间载体质粒。利用上述酶切位点对该片段进行了亚克隆和序列分析,结果表明,本研究克隆的RDV中国流行林基因组第10号片段的编码区与日本流行株的相应区域比较,核酸的同源率为96.03%,编码的氨基酸的同源率为97.17%。 相似文献
958.
Intensified plant N and C pool with more available nitrogen under experimental warming in an alpine meadow ecosystem 下载免费PDF全文
Fei Peng Xian Xue Quangang You Manhou Xu Xiang Chen Jian Guo Tao Wang 《Ecology and evolution》2016,6(23):8546-8555
Nitrogen (N) availability is projected to increase in a warming climate. But whether the more available N is immobilized by microbes (thus stimulates soil carbon (C) decomposition), or is absorbed by plants (thus intensifies C uptake) remains unknown in the alpine meadow ecosystem. Infrared heaters were used to simulate climate warming with a paired experimental design. Soil ammonification, nitrification, and net mineralization were obtained by in situ incubation in a permafrost region of the Qinghai‐Tibet Plateau (QTP). Available N significantly increased due to the stimulation of net nitrification and mineralization in 0–30 cm soil layer. Microbes immobilized N in the end of growing season in both warming and control plots. The magnitude of immobilized N was lower in the warming plots. The root N concentration significantly reduced, but root N pool intensified due to the significant increase in root biomass in the warming treatment. Our results suggest that a warming‐induced increase in biomass is the major N sink and will continue to stimulate plant growth until plant N saturation, which could sustain the positive warming effect on ecosystem productivity. 相似文献
959.
采用碱裂解法、化学改良方法、CTAB法、酚氯法等4种方法提取从泉州红树林沉积物中筛选出多环芳烃降解菌群YL的质粒,并分别转化至大肠杆菌感受态细胞,然后采用富集筛选的手段,最终确立最佳方案得到一组质粒转化菌群.该转化菌群可以利用芘作为其生长的惟一碳源和能源,并能在21 d内将50 mg·L-1的芘降解85.69%.而受体菌E.coli DH5α的芘降解率仅为2.006%.由此可以证明,降解质粒已成功转化进宿主细胞,并发挥降解作用.YL的质粒含有降解芘的基因. 相似文献
960.
Jukka Kekäläinen Geir Rudolfsen Matti Janhunen Lars Figenschou Nina Peuhkuri Niina Tamper Raine Kortet 《BMC evolutionary biology》2010,10(1):20