全文获取类型
收费全文 | 34768篇 |
免费 | 599篇 |
国内免费 | 1029篇 |
专业分类
系统科学 | 848篇 |
丛书文集 | 679篇 |
教育与普及 | 385篇 |
理论与方法论 | 119篇 |
现状及发展 | 5875篇 |
研究方法 | 800篇 |
综合类 | 27371篇 |
自然研究 | 319篇 |
出版年
2022年 | 372篇 |
2021年 | 368篇 |
2016年 | 258篇 |
2015年 | 433篇 |
2014年 | 672篇 |
2013年 | 815篇 |
2012年 | 951篇 |
2011年 | 1302篇 |
2010年 | 827篇 |
2009年 | 830篇 |
2008年 | 1058篇 |
2007年 | 1142篇 |
2006年 | 989篇 |
2005年 | 950篇 |
2004年 | 860篇 |
2003年 | 763篇 |
2002年 | 782篇 |
2001年 | 1255篇 |
2000年 | 1282篇 |
1999年 | 1403篇 |
1998年 | 886篇 |
1997年 | 959篇 |
1996年 | 884篇 |
1995年 | 706篇 |
1994年 | 714篇 |
1993年 | 581篇 |
1992年 | 829篇 |
1991年 | 731篇 |
1990年 | 729篇 |
1989年 | 716篇 |
1988年 | 643篇 |
1987年 | 494篇 |
1986年 | 384篇 |
1985年 | 348篇 |
1984年 | 278篇 |
1979年 | 502篇 |
1978年 | 391篇 |
1977年 | 365篇 |
1976年 | 302篇 |
1975年 | 348篇 |
1974年 | 496篇 |
1973年 | 376篇 |
1972年 | 386篇 |
1971年 | 491篇 |
1970年 | 607篇 |
1969年 | 413篇 |
1968年 | 448篇 |
1967年 | 377篇 |
1966年 | 384篇 |
1965年 | 259篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Thyroid cancer after Chernobyl. 总被引:17,自引:0,他引:17
82.
估计两个单属性关系在连接属性上取相同值的个数的方法有两种:静态估计法和动态估计法.本文利用不精确性推理模型对这两种方法的可信度定量地进行讨论,并用具体例子进行说明. 相似文献
83.
84.
To validate procedures of rational drug design, it is important to develop computational methods that predict binding sites between a protein and a ligand molecule. Many small molecules have been tested using such programs, but examination of protein-protein and peptide-protein interactions has been sparse. We were able to test such applications once the structures of both the maltose-binding protein (MBP) and the ligand-binding domain of the aspartate receptor, which binds MBP, became available. Here we predict the binding site of MBP to its receptor using a 'binary docking' technique in which two MBP octapeptide sequences containing mutations that eliminate maltose chemotaxis are independently docked to the receptor. The peptides in the docked solutions superimpose on their original positions in the structure of MBP and allow the formation of an MBP-receptor complex. The consistency of the computational and biological results supports this approach for predicting protein-protein and peptide-protein interactions. 相似文献
85.
Targeted disruption of the mouse transforming growth factor-beta 1 gene results in multifocal inflammatory disease. 总被引:149,自引:0,他引:149
M M Shull I Ormsby A B Kier S Pawlowski R J Diebold M Yin R Allen C Sidman G Proetzel D Calvin 《Nature》1992,359(6397):693-699
Transforming growth factor-beta 1 (TGF-beta 1) is a multifunctional growth factor that has profound regulatory effects on many developmental and physiological processes. Disruption of the TGF-beta 1 gene by homologous recombination in murine embryonic stem cells enables mice to be generated that carry the disrupted allele. Animals homozygous for the mutated TGF-beta 1 allele show no gross developmental abnormalities, but about 20 days after birth they succumb to a wasting syndrome accompanied by a multifocal, mixed inflammatory cell response and tissue necrosis, leading to organ failure and death. TGF-beta 1-deficient mice may be valuable models for human immune and inflammatory disorders, including autoimmune diseases, transplant rejection and graft versus host reactions. 相似文献
86.
87.
许朝光 《河北师范大学学报(自然科学版)》1992,(3)
本文系上篇论文[3]的续篇。在其中,进一步论述了2—距离空间中集值映射不动点的一系列结果。 相似文献
88.
通过交流磁化率和X-ray衍射分析,对用固态反应法制备的HoBa2Cu3Ox超导体的超导电性进行了研究.实验结果表明:随淬火温度的升高.由正交相(123相)向介于正交和四方相之间的过渡相变化;超导转变温度Tc(0)(零场下)从90K降到38.5K;交流磁化率虚部峰值温Tp(H)随附加直流磁场的增加而降低,Tp与Hdc之间的关系偏离[1一Tp(H)/丁(0)]∞H^2/3规律. 相似文献
89.
90.
Abnormal pattern detected in fragile-X patients by pulsed-field gel electrophoresis. 总被引:26,自引:0,他引:26
The fragile-X syndrome is the most frequent inherited form of mental retardation, with an incidence of 1 in 1,500 males. It is characterized by the presence of a fragile site at Xq27.3 induced in vitro by folate deprivation or by inhibitors of deoxynucleotide synthesis. Its mode of inheritance is unusual for an X-linked trait, with incomplete penetrance in both males and females. Some phenotypically normal males transmit the mutation to all their daughters who rarely express any symptoms, but penetrance is high in sons and daughters of these carrier women. Genetic and physical mapping of the Xq27-q28 region has confirmed that the disease locus is located at or very near the fragile site. Hypotheses proposed to account for the abnormalities in the inheritance of the disease include sequence rearrangements by meiotic recombination or a mutation that affects reactivation of an inactive X chromosome during differentiation of female germ cells. To detect such rearrangements, or methylation changes that may reflect a locally inactive X chromosome, we used pulsed-field gel analysis of DNA from fragile-X patients with probes close to the fragile-X locus. The probe Do33 (DXS465) detected abnormal patterns in fragile-X patients, but not in normal controls or in non-expressing male transmitters. 相似文献