全文获取类型
收费全文 | 22843篇 |
免费 | 1347篇 |
国内免费 | 798篇 |
专业分类
24988篇 |
出版年
2023年 | 357篇 |
2022年 | 542篇 |
2021年 | 625篇 |
2020年 | 641篇 |
2019年 | 874篇 |
2018年 | 901篇 |
2017年 | 560篇 |
2016年 | 557篇 |
2015年 | 661篇 |
2014年 | 1395篇 |
2013年 | 1773篇 |
2012年 | 1043篇 |
2011年 | 1410篇 |
2010年 | 1002篇 |
2009年 | 1081篇 |
2008年 | 1101篇 |
2007年 | 1124篇 |
2006年 | 962篇 |
2005年 | 851篇 |
2004年 | 723篇 |
2003年 | 634篇 |
2002年 | 525篇 |
2001年 | 339篇 |
2000年 | 316篇 |
1999年 | 315篇 |
1998年 | 279篇 |
1997年 | 235篇 |
1996年 | 234篇 |
1995年 | 205篇 |
1994年 | 198篇 |
1993年 | 198篇 |
1992年 | 169篇 |
1991年 | 160篇 |
1990年 | 133篇 |
1989年 | 114篇 |
1988年 | 99篇 |
1987年 | 92篇 |
1986年 | 92篇 |
1985年 | 189篇 |
1984年 | 361篇 |
1983年 | 297篇 |
1982年 | 283篇 |
1981年 | 215篇 |
1980年 | 189篇 |
1979年 | 163篇 |
1978年 | 133篇 |
1977年 | 134篇 |
1976年 | 122篇 |
1975年 | 101篇 |
1973年 | 105篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Prof. Dr. Franz M. Wuketits 《当今生物学》2011,41(5):334-340
The Natural History of Good and Evil Morality is a result of evolution by natural selection. It facilitates the stability of groups which gives advantage to the involved individuals and is thus, at least in some basic form – as moral‐analogous behavior –, also developed in nonhuman primates and other mammalian species. Of crucial importance is reciprocal altruism that, however, for long periods of time applied only to – and was favored by natural selection in – comparatively small groups. Its extension therefore meets fundamental difficulties, and we have to consider limitations to morality. From the perspective of evolutionary theory (evolutionary ethics) humans by nature are neither good nor evil. Under certain cultural constraints they can develop enormous destructive potentials, but also experience stimuli for cooperative and helping behavior. 相似文献
82.
N E Owen 《Biochemical and biophysical research communications》1984,125(2):500-508
The regulation of Na/K/Cl cotransport was investigated in vascular smooth muscle cells. That a Na/K/Cl cotransport system exists was established by the finding that the ouabain insensitive K influx was sensitive to the "loop" diuretic bumetanide. Furthermore, bumetanide sensitive K influx was dependent upon the presence of both Na and Cl in the extracellular milieu. Bumetanide sensitive K influx was inhibited by agents which elevate cellular cyclic AMP levels, and to a lesser extent by agents which elevate cellular cyclic GMP levels. When serum, EGF or TPA was added, bumetanide sensitive K influx was enhanced. These results suggest that vascular smooth muscle cells have a ouabain insensitive, bumetanide sensitive Na/K/Cl cotransport system which is stimulated by serum, EGF or TPA and inhibited by cAMP or cGMP. 相似文献
83.
84.
Receptor-like kinases (RLKs) play important roles in multiple aspects of plant growth and development. As a member of the TNFR-like RLK subfamily, rice Crinkly4 (OsCR4) functions mainly in epidermal cell differentiation in many organs. Here we show that in addition to its essential role in epidermal cell differentiation in the palea and lemma, OsCR4 positively regulates rice culm elongation, similar to maize CR4. Although OsCR4 is an active kinase, like CR4 in maize and ACR4 in Arabidopsis, the conserved amino acid K532 in OsCR4 is not essential for its kinase activity in vitro. Whether other conserved amino acids are required for its kinase activity and the relationship between its activity and function in plant development remain to be investigated. 相似文献
85.
86.
87.
Shizuo Narimatsu Rika Kato Toshiharu Horie Satoshi Ono Michio Tsutsui Yoshiyasu Yabusaki Shigeru Ohmori Mitsukazu Kitada Takao Ichioka Noriaki Shimada Ryuichi Kato Tsutomu Ishikawa 《Chirality》1999,11(1):1-9
The enantioselectivity of 4‐hydroxylation of bunitrolol (BTL), a β‐adrenoceptor blocking drug, was studied in microsomes from human liver, human hepatoma (Hep G2) cells expressing CYP2D6, and lymphoblastoid cells expressing CYP2D6. Kinetics in human liver microsomes showed that the Vmax value for (+)‐BTL was 2.1‐fold that of (−)‐BTL, and that the Km value for (+)‐BTL was lower than that for the (−)‐antipode, resulting in the intrinsic clearance (Vmax/Km) of (+)‐BTL being 2.1‐fold over its (−)‐antipode. CYP2D6 (CYP2D6‐met) expressed in Hep G2 cells had a methionine residue at position 373 of the amino acid sequence and a rat‐type N‐terminal peptide (MELLNGTGLWSM) instead of the human‐type (MGLEALVPLAVIV), and showed enantioselectivity of [(+)‐BTL < (−)‐BTL] for the rate of BTL 4‐hydroxylation. In contrast, enantioselectivity [(+)‐BTL > (−)‐BTL] for Hep G2‐CYP2D6 (CYP2D6‐val) with a human‐type N‐terminal peptide that had a valine residue at 374, which corresponds to the methionine of the CYP2D6‐met variant, was the same as that for human liver microsomes. We further confirmed that CYP2D6‐met and CYP2D6‐val expressed in human lymphoblastoid cells, both of which have methionine and valine, respectively, at position 374 and a human‐type N‐terminal peptide, exhibited the same enantioselectivities as those obtained from CYP2D6‐met and CYP2D6‐val expressed in the Hep G2 cell system. These results indicate that the amino acid at 374 of CYP2D6 is one of the key factors influencing the enantioselectivity of BTL 4‐hydroxylation. Chirality 11:1–9, 1999. © 1999 Wiley‐Liss, Inc. 相似文献
88.
《Bioorganic & medicinal chemistry letters》2020,30(4):126906
The prevalence of Zika virus (ZIKV) has become widespread in recent years. ZIKV infection is associated with severe congenital CNS malformations in both newborns and adults. However, neither vaccines nor therapeutics are available to control ZIKV infection until now. We started by hit screening our in-house small molecule library, then designed, synthesized, and evaluated a new class of 1, 4-bibenzylsubstituted piperazine derivatives for their cytopathic effect (CPE) protection effect in a ZIKV-infected Vero E6 cellular assay. A preliminary structure–activity relationship study identified five novel 4-amino-2-(4-benzylpiperazin-1-yl)methylbenzonitrile analogs with obvious CPE reduction effects against ZIKV at micromolar concentrations. Moreover, compound 3p exerted a significant antiviral effect on both Zika RNA replication and virus protein expression in a dose-dependent manner at low micromolar concentrations. This study demonstrated the potential of a novel 4-amino-2-(4-benzylpiperazin-1-yl)methylbenzonitrile scaffold for the development of anti-ZIKV candidates. 相似文献
89.
Moya M. Smith Zerina Johanson Thomas Butts Rolf Ericsson Melinda Modrell Frank J. Tulenko Marcus C. Davis Gareth J. Fraser 《Proceedings. Biological sciences / The Royal Society》2015,282(1805)
Ray-finned fishes (Actinopterygii) are the dominant vertebrate group today (+30 000 species, predominantly teleosts), with great morphological diversity, including their dentitions. How dental morphological variation evolved is best addressed by considering a range of taxa across actinopterygian phylogeny; here we examine the dentition of Polyodon spathula (American paddlefish), assigned to the basal group Acipenseriformes. Although teeth are present and functional in young individuals of Polyodon, they are completely absent in adults. Our current understanding of developmental genes operating in the dentition is primarily restricted to teleosts; we show that shh and bmp4, as highly conserved epithelial and mesenchymal genes for gnathostome tooth development, are similarly expressed at Polyodon tooth loci, thus extending this conserved developmental pattern within the Actinopterygii. These genes map spatio-temporal tooth initiation in Polyodon larvae and provide new data in both oral and pharyngeal tooth sites. Variation in cellular intensity of shh maps timing of tooth morphogenesis, revealing a second odontogenic wave as alternate sites within tooth rows, a dental pattern also present in more derived actinopterygians. Developmental timing for each tooth field in Polyodon follows a gradient, from rostral to caudal and ventral to dorsal, repeated during subsequent loss of teeth. The transitory Polyodon dentition is modified by cessation of tooth addition and loss. As such, Polyodon represents a basal actinopterygian model for the evolution of developmental novelty: initial conservation, followed by tooth loss, accommodating the adult trophic modification to filter-feeding. 相似文献
90.
Chathuraka T Jayasuriya Mary B Goldring Richard Terek Qian Chen 《Arthritis research & therapy》2012,14(5):R197