全文获取类型
收费全文 | 6436篇 |
免费 | 586篇 |
国内免费 | 502篇 |
出版年
2024年 | 16篇 |
2023年 | 157篇 |
2022年 | 156篇 |
2021年 | 214篇 |
2020年 | 276篇 |
2019年 | 372篇 |
2018年 | 307篇 |
2017年 | 253篇 |
2016年 | 235篇 |
2015年 | 221篇 |
2014年 | 404篇 |
2013年 | 517篇 |
2012年 | 259篇 |
2011年 | 323篇 |
2010年 | 262篇 |
2009年 | 291篇 |
2008年 | 320篇 |
2007年 | 317篇 |
2006年 | 301篇 |
2005年 | 265篇 |
2004年 | 252篇 |
2003年 | 239篇 |
2002年 | 184篇 |
2001年 | 153篇 |
2000年 | 115篇 |
1999年 | 105篇 |
1998年 | 118篇 |
1997年 | 89篇 |
1996年 | 88篇 |
1995年 | 75篇 |
1994年 | 79篇 |
1993年 | 62篇 |
1992年 | 73篇 |
1991年 | 47篇 |
1990年 | 27篇 |
1989年 | 35篇 |
1988年 | 26篇 |
1987年 | 34篇 |
1986年 | 31篇 |
1985年 | 37篇 |
1984年 | 24篇 |
1983年 | 24篇 |
1982年 | 26篇 |
1981年 | 15篇 |
1980年 | 20篇 |
1979年 | 13篇 |
1978年 | 15篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 10篇 |
排序方式: 共有7524条查询结果,搜索用时 15 毫秒
991.
A general statistical methodology for analysis of selectivity data from any type of fishing gear is presented. This formal statistical modelling of selectivity is built on explicit definitions of the selection process and specification of underlying assumptions and limitations, and this gives the resulting estimates of gear selectivity (and possibly fishing power) a clear interpretation. Application of the methodology to studies using subsampled catch data and to towed gears having windows or grids is outlined, and examples applied to passive nets and towed gears are presented. The analysis of data from replicate deployments is covered in detail, with particular regard to modelling the fixed and random effects of between-haul variation. Recent developments on the design of selectivity experiments are introduced and demonstrated. 相似文献
992.
Relating structure to thermodynamics: the crystal structures and binding affinity of eight OppA-peptide complexes. 下载免费PDF全文
T. G. Davies R. E. Hubbard J. R. Tame 《Protein science : a publication of the Protein Society》1999,8(7):1432-1444
The oligopeptide-binding protein OppA provides a useful model system for studying the physical chemistry underlying noncovalent interactions since it binds a variety of readily synthesized ligands. We have studied the binding of eight closely related tripeptides of the type Lysine-X-Lysine, where X is an abnormal amino acid, by isothermal titration calorimetry (ITC) and X-ray crystallography. The tripeptides fall into three series of ligands, which have been designed to examine the effects of small changes to the central side chain. Three ligands have a primary amine as the second side chain, two have a straight alkane chain, and three have ring systems. The results have revealed a definite preference for the binding of hydrophobic residues over the positively charged side chains, the latter binding only weakly due to unfavorable enthalpic effects. Within the series of positively charged groups, a point of lowest affinity has been identified and this is proposed to arise from unfavorable electrostatic interactions in the pocket, including the disruption of a key salt bridge. Marked entropy-enthalpy compensation is found across the series, and some of the difficulties in designing tightly binding ligands have been highlighted. 相似文献
993.
Lim Amareth Saderholm Matthew J. Kroll Mathias Yan Yibing Erickson Bruce W. Guy Philippe A. Anderegg Robert J. Makhov Alexander M. Griffith Jack D. 《International journal of peptide research and therapeutics》1999,6(1):3-14
Summary The inverse protein-folding problem has been explored by designing de novo the betabellin target structure (a 64-residue β-sandwich
protein), synthesizing a 32-residue peptide chain (HSLTAKIpkLTFSIAphTYTCAVpkYTAKVSH, wherep=DPro,k=DLys, andh=DHis) that might fold into this structure, and studying how its disulfide-bridged form (betabellin 15D) folds in 10 mM ammonium
acetate with and without Cu2+. Circular dichroic spectropolarimetry indicated that at pH 5.8, 6.4, or 6.7 betabellin 15D exhibited β-sheet structure in
the presence of Cu2+ but not in its absence. Electrospray mass spectrometry demonstrated that at pH 6.3 each molecule of betabellin 15D bound
one or two Cu(II) ions. Electron microscopy showed that at pH 6.7 betabellin 15D formed short broad fibrils in the presence
of Cu2+ but not in its absence. The observed width of the fibrils (7±2 nm) was consistent with the width (6.8nm) of a structural
model of a fibril that contained two adjacent rows of betabellin 15D β-sandwiches joined lengthwise by multiple intersheet
hydrogen bonds and widthwise by multiple Cu(II)-imidazole bonds. Electron paramagnetic resonance spectrometry revealed that
some pairs of Cu(II) ions in a Cu(II)/betabellin 15D complex were magnetically coupled, which is consistent with the structural
model of the Cu(II)/betabellin 15D fibril. 相似文献
994.
同源模建人微小纤溶酶原(microplasminogen ,mplg)的三维结构,建立葡激酶(staphylokinase,Sak),mplg计算机分子对接的结构模型,模型与已有的实验结果基本相符。为研究葡激酶N端结构与功能的关系,进一步改造葡激酶分子,根据复合物结构模型设计了N端缺失15个氨基酸的葡激酶突变体。 相似文献
995.
LEBEL, CARL, AMY BOURDEAU, DAVID LAU, AND PAMELA HUNT. Biologic response to peripheral and central administration of recombinant human leptin in dogs. Obes Res. Objective: Because leptin is believed to act within the central nervous system, the objective of this study was to test that presumption by comparing the biologic responses to recombinant human leptin (rHuLeptin) when delivered either subcutaneously or intrathecally in a large animal species, the beagle dog. Methods and Procedures: Adult beagle dogs were used for all studies (n = 3 to 14). Treatment with rHuLeptin was either as daily subcutaneous or intermittent intrathecal injections. Results: Subcutaneously administered rHuLeptin was absorbed with peak concentrations appearing at 2 to 4 hours. After intrathecal administration, cerebral spinal fluid concentrations declined in a bi-phasic manner with a terminal half-life of ?6 to 8 hours. When lean beagles were given leptin subcutaneously, at 0. 05 to 5 gkglday for up to 6 months, reductions in body weight (up to 30%) and food intake (up to 75%) were observed. Body fat loss was observed in both lean and obese dogs, and confirmed by dual energy X-ray absorptiometry and histology of adipose tissue. When rHuleptin was delivered intrathecally at 4 to 1000 μg/dose for up to 3 months, the primary effects observed were reductions in body weight and food intake. In general all findings reported in the intrathecal studies were consistent with those noted in the subcutaneous studies; however, the required intrathecal dose was substantially lower than that for subcutaneous delivery. Discussion: These studies demonstrate that both subcutaneous and intrathecal treatment of rHuLeptin was associated with effects on body weight, food intake, and body fat in dogs. These results support the concept that the central nervous system is the probable primary site of action for leptin and suggest that rHuLeptin has similar physiologic activities that influence body weight, body fat, and metabolism in large animals to those reported previously in rodents. 相似文献
996.
997.
A new Monosulcate pollen has been discovered from the upper partof Lower Cretaceous deposits of Hubei, Jiangsu, Jingxi and Hebei Provinces. Thesepollens have a monosulcate on their distal surface with salient features and differ fromCycadopites and Benettites. We call them Zhonghuapollis gen. nov. They are widespread geographically and only restricted to the later Early Cretaceous deposits, so very useful in stratigraphical dividing and correlation of this deposits. 相似文献
998.
温、湿度对亚洲玉米螟成虫繁殖力及寿命的影响 总被引:10,自引:0,他引:10
温度和湿度的变化对亚洲玉米螟0strinia furnacalis(Guenee)成虫的交配和产卵及寿命都具有极显著的影响。在16℃~32℃和RH20%~100%的温湿范围中,亚洲玉米螟成虫繁殖力在20℃~28℃恒温和RH70%~100%的温湿组合中较大,其中在24℃恒温和28℃~20℃变温与RH90%~100%的组合中为最大,在32℃和RH20%的组合中为最小。单雌抱卵量、产卵量和产出卵率及交配次数均与温度呈抛物线曲线关系,与湿度呈正相关。温、湿度对成虫繁殖力具有极显著的交互作用。成虫寿命与温湿度密切相关,温度越高,成虫寿命越短;而湿度越高,成虫寿命越长。但雄蛾比雌蛾较耐低湿,在16℃~24℃下雄蛾寿命比雌蛾较长。此外,雄蛾较强的交配能力可促进卵的发育和产出。以上结果对玉米螟种群动态消长的分析和预测预报提供了参考依据。 相似文献
999.
S Basu M Khanra B Dash J Majumdar J Biswas P Chaudhuri 《Cancer immunology, immunotherapy : CII》1999,16(3):199-203
We performed a retrospective analysis on the effect of neoadjuvant chemotherapy with three cycles of methotrexate (100 mg/m2 on day 1), cisplatin (90 mg/m2 on day 1) and bleomycin (20 mg/m2 on day 1–5) with 21 d gap between each cycle in 44 patients with advanced squamous cell carcinoma of the cheek, lip and tongue
followed by surgery and adjuvant chemotherapy consisting of cisplatin (90 mg/m2 on day 1), Mitomycin C (6 mg/m2 on day 1) and 5-fluorouracil (1000 mg/m2 120 h continuous infusion from day 1) repeated every 3 weeks for three cycles.
Following induction chemotherapy, complete response was observed in 11 out of 44 patients (25%), and a partial response in
a further 28 patients (64%).
The overall median survival of all patients was 29 months and those in stage III and stage IV were 30 and 15 months respectively
(P<0.001). The median duration of the time to relapse in patients who responded to adjuvant chemotherapy was 28 months.
The main toxic effect was vomiting followed by hematological toxicity. No treatment-related deaths occurred.
The regimen showed a significant response, encouraging median survival and a good tolerability profile. 相似文献
1000.