全文获取类型
收费全文 | 89942篇 |
免费 | 1755篇 |
国内免费 | 1425篇 |
专业分类
化学 | 32911篇 |
晶体学 | 932篇 |
力学 | 7224篇 |
综合类 | 110篇 |
数学 | 33259篇 |
物理学 | 18686篇 |
出版年
2023年 | 191篇 |
2022年 | 341篇 |
2021年 | 373篇 |
2020年 | 403篇 |
2019年 | 400篇 |
2018年 | 10671篇 |
2017年 | 10491篇 |
2016年 | 6548篇 |
2015年 | 1333篇 |
2014年 | 964篇 |
2013年 | 1238篇 |
2012年 | 4845篇 |
2011年 | 11534篇 |
2010年 | 6334篇 |
2009年 | 6662篇 |
2008年 | 7331篇 |
2007年 | 9394篇 |
2006年 | 825篇 |
2005年 | 1785篇 |
2004年 | 1986篇 |
2003年 | 2382篇 |
2002年 | 1459篇 |
2001年 | 570篇 |
2000年 | 506篇 |
1999年 | 396篇 |
1998年 | 345篇 |
1997年 | 275篇 |
1996年 | 347篇 |
1995年 | 235篇 |
1994年 | 198篇 |
1993年 | 205篇 |
1992年 | 148篇 |
1991年 | 152篇 |
1990年 | 119篇 |
1989年 | 140篇 |
1988年 | 108篇 |
1987年 | 100篇 |
1986年 | 109篇 |
1985年 | 97篇 |
1984年 | 79篇 |
1983年 | 62篇 |
1982年 | 64篇 |
1981年 | 72篇 |
1980年 | 71篇 |
1979年 | 65篇 |
1978年 | 60篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
891.
892.
893.
稀土离子(Ⅲ)与牛血清白蛋白作用的紫外光谱 总被引:18,自引:1,他引:18
用紫外光谱研究了稀土离子(Ⅲ)与牛血清白蛋白(BSA)的作用.14种稀土离子均使BSA~280um特征吸收峰强增加,诱导BSA构象发生改变.紫外差谱结果表明,只有氧原子参加与稀土配位.BSA与稀土配位基团为亲水外壳的氨基酸波基和肽键上的C=O基团. 相似文献
894.
Rahul Mukerjee 《The Journal of the Operational Research Society》1982,33(10):957-959
The problem of minimising E(X) subject to the constraints X ? 0, P(X ? b) ? a(0 < a < 1) has been considered, where b is a non-negative random variable with continuous probability distribution. A necessary and sufficient condition for randomised decisions to be superior to the non-randomised one has been derived. 相似文献
895.
A pseudo-first-order catalytic mechanism in which both reactant and product of a redox reaction are strongly immobilized
on an electrode surface is theoretically analysed under conditions of square-wave (SWV) and staircase cyclic voltammetry (SCV).
A mathematical procedure is developed under diffusionless conditions. The relationships between the properties of the voltammetric
response and both the kinetic parameters of the redox reaction and the parameters of the excitation signal are studied. The
phenomenon of the quasi-reversible maximum is discussed. A comparative study between SWV and SCV is presented and the limitations
and advantages of both techniques, from analytical and kinetic points of view, are discussed. The theoretical predictions
are experimentally confirmed by the redox reaction of azobenzene in the presence of hydrogen peroxide as an oxidizing agent.
Electronic Publication 相似文献
896.
A facile total synthesis of (+)-hernandulcin (1) was accomplished from (−)-isopulegol in 6 steps with 15% overall yield. Epoxidation of (−)-isopulegol with m-chloroperbenzoic acid followed by opening of the epoxide 3a with prenyl Grignard afforded the tertiary alcohol 4a with correct C-6 and C-1′ stereochemistry as a major product. Oxidation of the secondary alcohol in compound 4a to the ketone 5a was accomplished in high yield by using TPAP and N-methylmorpholine N-oxide. Conversion of the ketone 5a to α,β-unsaturated ketone via organoselenium intermediate gave (+)-hernandulcin (1). This method was also successfully applied to the synthesis of (+)-epihernandulcin (2). 相似文献
897.
This review of ion-selective electrodes is arranged in the same way as Parts I and II. The continuous growth of the whole subject should be noted. Theory has particularly progressed through mechanistic studies. Among new types of electrodes, ISFET systems have become important. Among new applications of both solid and liquid membrane electrodes, the fluoride electrode still predominates, closely followed by potassium electrodes. In the field of biological and medical applications, the steady growth is significant. More than 800 papers published between mid-1976 and the end of 1978 are mentioned in the review. 相似文献
898.
A new ligand, 2-carboxybenzaldehyde-(4’-hydroxy)benzoylhydrazone(H2L) and its ZnII and NiII complexes have been synthesized and characterized on the basis of elemental analyses, molar conductivities, 1H-NMR, IR spectra and thermal analyses. In addition, DNA-binding properties of these two metal complexes were investigated
using spectrometric titrations, ethidium bromide displacement experiments, and viscosity measurements. The results show that
the two complexes, especially the NiII complex, strongly bind with calf-thymus DNA, presumably via an intercalation mechanism. The intrinsic binding constants of the ZnII and NiII complexes with DNA are 2.46 × 105 and 7.94 × 105
M
−1, respectively. 相似文献
899.
Yu-Fen Zhao De-Qing Zhang Chu-Biao Xue Jia-Ning Zeng Gai-Jiao Ji 《Journal of mass spectrometry : JMS》1991,26(5):510-513
Positive ion fast atom bombardment mass spectrometry of N-diisopropyloxyphosphoryl dipeptides and tripeptides showed a novel cleavage pattern in that only the N-phosphoryl fragment ions gave intense peaks while the C-terminal series of ions was suppressed. The base peak was the N-phosphoryl imino ion responding to the N-terminal residue. These advantages are superior to those of other types of N-protecting groups. 相似文献
900.
YingXinLIU ZuoJunWEI JiXiangCHEN JiYanZHANG XinXueLI XiongHuiWEI 《中国化学快报》2005,16(4):531-533
A novel lanthana-promoted nickel catalyst supported on silica for the liquid phase hydrogenation of m-dinitrobenzene to m-phenylenediamine was prepared by an incipient wetness sequential impregnation method. It was found that Ni-La/SiO2 catalyst exhibited high activity and stability for m-dinitrobenzene hydrogenation. Over this catalyst, the conversion of m-dinitrobenzene and the yield of m-phenylenediamine were up to 97.1% and 93.5%, respectively,at 373 K and 2.6 MPa hydrogen pressure after reaction for 1 h. 相似文献