首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2896篇
  免费   482篇
  国内免费   301篇
化学   2226篇
晶体学   71篇
力学   126篇
综合类   31篇
数学   294篇
物理学   931篇
  2024年   6篇
  2023年   63篇
  2022年   102篇
  2021年   109篇
  2020年   191篇
  2019年   150篇
  2018年   121篇
  2017年   101篇
  2016年   146篇
  2015年   156篇
  2014年   169篇
  2013年   188篇
  2012年   239篇
  2011年   236篇
  2010年   186篇
  2009年   158篇
  2008年   188篇
  2007年   140篇
  2006年   174篇
  2005年   129篇
  2004年   95篇
  2003年   91篇
  2002年   86篇
  2001年   57篇
  2000年   50篇
  1999年   46篇
  1998年   33篇
  1997年   33篇
  1996年   41篇
  1995年   30篇
  1994年   12篇
  1993年   11篇
  1992年   11篇
  1991年   29篇
  1990年   9篇
  1989年   9篇
  1988年   5篇
  1987年   4篇
  1986年   9篇
  1985年   6篇
  1984年   6篇
  1983年   6篇
  1982年   8篇
  1981年   5篇
  1980年   6篇
  1979年   7篇
  1978年   4篇
  1977年   4篇
  1976年   4篇
  1975年   4篇
排序方式: 共有3679条查询结果,搜索用时 15 毫秒
31.
用硒与尿素化合,新生的由杂环有机硒所组成的Zs-93硒剂治疗移植性S180肉瘤,有显著的抑瘤作用(P<0.01),其作用表现出一定的剂量效应,以5μg/只小鼠为最适,抑瘤率达60.76%,治疗组小鼠的T细胞、SOD活性均有增强。  相似文献   
32.
Intracellular delivery of enzymes is essential for protein-based diagnostic and therapeutic applications. Protein-spherical nucleic acids (ProSNAs) defined by protein core and dense shell of oligonucleotides have been demonstrated as a promising vehicle-free enzyme delivery platform. In this work, we reported a crosslinking strategy to vastly improve both delivery efficiency and intracellular sensor performance of ProSNA. By assembling individual ProSNA with lactate oxidase (LOX) core into a nanoscale particle, termed as crosslinked SNA (X-SNA), the enzyme delivery efficiency increased up to 5–6 times higher. The LOX X-SNA was later demonstrated as a ratiometric probe for quantitative detection of lactate in living cells. More importantly, X-SNA probe showed significantly improved sensor performance with signal-to-noise ratio 4 times as high as ProSNA when detecting intracellular lactate.

By crosslinking protein spherical nucleic acid (SNA) into a supramolecular architecture X-SNA, the intracellular enzyme delivery efficiency was significantly enhanced, showing 3–4 times higher signal-to-noise ratio in detecting intracellular lactate.  相似文献   
33.
Polonium-210 has been measured in the soft parts of Anadara granosa purchased at Kuala Selangor, West Coast of Malaysia in August 2001, April 2002 and September 2002. It is shown that 210Po is non-uniformly distributed within cockles of various sizes (i.e., 2.5, 3.0, 3.5 and 4.0 cm of shell length) and the concentration of 210Po in the soft parts of cockle was significantly different (p<0.05) due to sampling date. The highest value was observed in the smallest cockle with a shell length of 2.5 cm (411.6±26.16 Bq/g dry wt.). It is clear that there is an allometric relationship between 210Po activity concentration and individual cockle weight. This may reflect on the differences of metabolic rate and growth age of cockles. The mean activity concentration of 210Po measured in Kuala Selangor filtered water were 1.75±0.17, 0.79±0.08 and 1.13±0.20 Bq/kg for August 2001, April 2002 and September 2002, respectively. The yield concentration factors for 210Po in the soft parts of cockles varies from 27.3. 103 to 106.9. 103. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
34.
In the EPR spectra of 17O2? adsorbed on MgO, the hyperfine lines due to 17O(I = 52) have been used to monitor the isotopic exchange with gas phase oxygen. The predicted behaviour of the different possible mechanisms (place exchange and/or isotopic exchange) is compared with the experimental results which show that, on MgO at room temperature, isotopic exchange occurs via an intermediate species which is tentatively identified as O4?.  相似文献   
35.
质谱法测定冰毒   总被引:1,自引:1,他引:1  
采用直接进样化学电离(CI)质谱法,配合电子轰击(EI)及气相色谱-质谱联用(GC/MS)技术,测定了冰毒及其制备过程中的副产品与中间产物,为刑侦破案提供了依据。  相似文献   
36.
Cu, Zn─SOD酶模型化合物催化O2歧化作用的研究   总被引:4,自引:2,他引:4  
为了解Cu,Zn-SOD酶结构和功能关系,尤其是Cu周围配位构型对催化O^-2歧化活性的影响,本文用NBT法测定了Cu,Zn-SOD酶和两个Cu-im-Zn模型配合及相应单核配合物催化O^_2歧化的活性,结果表明不同咪唑桥联方式和不同配位构型的化合物催化O^-2歧化的活性明显不同。  相似文献   
37.
In the title complex, [Zn(C12H6O4)(H2O)]n, a ZnII polymer based on naphthalene‐1,8‐dicarboxylate (1,8‐nap), the ZnII atoms adopt an elongated octahedral coordination geometry. A zigzag chain is formed by μ2‐aqua ligands and μ2‐carboxylate groups of the 1,8‐nap ligands. Adjacent parallel chains are further linked by 1,8‐nap ligands, forming a twisted two‐dimensional layer structure along the (100) plane.  相似文献   
38.
Denote by * n the set of all k *-cycle resonant hexagonal chains with n hexagons. For any B n * n , let m(B n ) and i(B n ) be the numbers of matchings (=the Hosoya index) and the number of independent sets (=the Merrifield–Simmons index) of B n , respectively. In this paper, we give a characterization of the k *-cycle resonant hexagonal chains, and show that for any B n * n , m(H n )m(B n ) and i(H n )i(B n ), where H n is the helicene chain. Moreover, equalities hold only if B n =H n .  相似文献   
39.
A series of Bcl-x(L)/Bak antagonists, based on a terephthalamide scaffold, was designed to mimic the alpha-helical region of the Bak peptide. These molecules showed favorable in vitro activities in disrupting the Bcl-x(L)/Bak BH3 domain complex (terephthalamides 9 and 26, K(i) = 0.78 +/- 0.07 and 1.85 +/- 0.32 microM, respectively). Extensive structure-affinity studies demonstrated a correlation between the ability of terephthalamide derivatives to disrupt Bcl-x(L)/Bak complex formation and the size of variable side chains on these molecules. Treatment of human HEK293 cells with the terephthalamide derivative 26 resulted in disruption of the Bcl-x(L)/Bax interaction in whole cells with an IC(50) of 35.0 microM. Computational docking simulations and NMR experiments suggested that the binding cleft for the BH3 domain of the Bak peptide on the surface of Bcl-x(L) is the target area for these synthetic inhibitors.  相似文献   
40.
原位沉析法制备磁性氧化铁羟基磷灰石/壳聚糖棒材   总被引:3,自引:0,他引:3  
首先通过化学沉淀法制备磁性氧化铁羟基磷灰石(Fe3O4/HA),然后以壳聚糖(CS)为基体,利用原位沉析法将Fe3O4/HA与CS复合,制得磁性Fe3O4/HA/CS复合材料.经XRD、粒径分布和PPMS测试,结果表明了Fe3O4/HA复合物的生成.系统研究了磁性Fe3O4/HA/CS棒材力学性能的影响因素,最终确定Fe3O4与HA质量比为3∶17,磁性Fe3O4/HA与CS质量比为9∶91时,棒材的力学性能最优,弯曲强度可达到87.0 MPa,弯曲模量1.57 GPa.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号