全文获取类型
收费全文 | 2129篇 |
免费 | 56篇 |
国内免费 | 12篇 |
专业分类
化学 | 1391篇 |
晶体学 | 9篇 |
力学 | 80篇 |
数学 | 236篇 |
物理学 | 481篇 |
出版年
2022年 | 15篇 |
2021年 | 25篇 |
2020年 | 35篇 |
2019年 | 28篇 |
2018年 | 17篇 |
2016年 | 39篇 |
2015年 | 24篇 |
2014年 | 38篇 |
2013年 | 99篇 |
2012年 | 96篇 |
2011年 | 153篇 |
2010年 | 58篇 |
2009年 | 68篇 |
2008年 | 113篇 |
2007年 | 111篇 |
2006年 | 106篇 |
2005年 | 114篇 |
2004年 | 88篇 |
2003年 | 73篇 |
2002年 | 68篇 |
2001年 | 34篇 |
2000年 | 37篇 |
1999年 | 26篇 |
1998年 | 24篇 |
1997年 | 24篇 |
1996年 | 24篇 |
1995年 | 18篇 |
1994年 | 24篇 |
1993年 | 17篇 |
1992年 | 27篇 |
1991年 | 25篇 |
1990年 | 31篇 |
1989年 | 22篇 |
1988年 | 26篇 |
1987年 | 23篇 |
1986年 | 24篇 |
1985年 | 34篇 |
1984年 | 24篇 |
1983年 | 22篇 |
1982年 | 17篇 |
1981年 | 24篇 |
1980年 | 20篇 |
1979年 | 24篇 |
1978年 | 23篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1975年 | 25篇 |
1974年 | 12篇 |
1973年 | 31篇 |
1970年 | 12篇 |
排序方式: 共有2197条查询结果,搜索用时 656 毫秒
61.
Karl S. Coleman Simon Turberville Malcolm L.H. Green 《Journal of organometallic chemistry》2005,690(3):653-658
A new ferrocenyl-N-heterocyclic carbene ligand precursor 1,1′-bis[(1-tert-butylimidazolium)-3-methyl]ferrocene dichloride has been synthesised and structurally characterised. The imidazolium salt was readily deprotonated in situ with KN(SiMe3)2 and reacted with [PdCl2 (cod)] to afford the structurally characterised palladium (II) complex trans-[PdCl2(C∧fc∧C)], where (cod) = 1,5-cyclooctadiene and (C∧fc∧C) = 1,1′-di-tert-butyl-3,3′-(1,1′-dimethyleneferrocenyl)-diimidazol-2-ylidene. 相似文献
62.
Simple binary solids can be found to adopt unprecedented structures when confined into nanometre-sized cavities, such as the inner cylindrical bore of single-walled carbon nanotubes (SWNT). In the case of the discussed Lal(x)@SWNT encapsulation composite, the Lal2 "crystal" fragment adopts the structure of bulk Lal3, with one third of the iodine positions unoccupied. A complete characterisation of the encapsulation composite was achieved using an enhanced digital restoration approach of high-resolution transmission electron microscopy (HRTEM) images. The resulting complex exit surface wave provides information about the precise structural data of both filling material and host SWNT, establishing the SWNT's chirality and thus enabling a prediction of the composite's overall electron-transport properties. 相似文献
63.
Evolutionary approaches are regularly used to isolate single molecules with desired activities from large populations of nucleic acids (approximately 10(15)). Several methods have also been developed to generate libraries of mRNA-encoded peptides and proteins for the in vitro selection of functional polypeptides. In principal, such mRNA encoding systems could be used with libraries of nonbiological polymers if the ribosome can be directed to polymerize tRNAs carrying unnatural amino acids. The fundamental problem is that current chemical aminoacylation systems cannot easily produce sufficient amounts of the numerous misacylated tRNAs required to synthesize a complex library of encoded polymers. Here, we show that bulk-aminoacylated tRNA can be transformed into N-monomethylated aminoacyl tRNA and translated. Because poly-N-methyl peptide backbones are refractory to proteases and are membrane permeable, our method provides an uncomplicated means of evolving novel drug candidates. 相似文献
64.
Minimizing molecular mobility for desiccation preservation of biologics close to ambient temperature using trehalose glasses require quantitative characterization of their enthalpic relaxation at various end water contents. Differential scanning calorimetry (DSC) was used to characterize three different water contents: 0%, 1.5% and 10% over a wide range of aging temperatures. Results showed the characteristic time (τ) varies both with the water content and the aging temperature. τ increased with lowered aging temperature but showed a non-monotonous relationship as a function of water content. Fragility of trehalose glasses was analyzed using thermophysical parameters obtained from relaxation studies. The study showed trehalose to be a fragile glass former at all water contents, with 0% water samples showing a relatively stronger glass. A compromise between molecular mobility and glass fragility led to an optimal water content close to 1.5% and an aging temperature close to room temperature. This would ensure a τ value of 9000 h, which corresponds to a storage period of a year. 相似文献
65.
The hyperfine fields Bhf (RbFe), Bhf (SrFe) and Bhf (YFe) have been determined by the low temperature nuclear orientation of dilute samples of83Rb,83,85Sr and85Ym in an iron lattice to be Bhf (RbFe)=+54 (10) kG, Bhf (SrFe)=(?)100 (30) kG and Bhf (YFe)=?226 (10) kG. These results are compared with recent calculations for these fields (1), (2). 相似文献
66.
[graph: see text] High-level ab initio calculations indicate that *CH3 addition to the sulfur center of S=P(Z)(Z')SCH3 (Z,Z' = CH3, CN, OCH3, Ph) is considerably less exothermic than addition to the corresponding RAFT agents, S=C(Z)SCH3. This suggests that dithiophosphinate esters may have only limited use in controlling free-radical polymerization, but should make excellent radical chain carriers in organic synthesis. The results cast doubt on the notion that phosphoranyl radicals are more "intrinsically" stabilized than carbon-centered radicals. 相似文献
67.
Miyagi K Sampson RW Sieber-Blum M Sieber F 《Journal of photochemistry and photobiology. B, Biology》2003,70(3):133-144
The purpose of this study was to determine in a preclinical purging model, how effective crystal violet-mediated photodynamic therapy (CV-PDT) is against solid tumor and drug-resistant mutant tumor cells, and if certain limitations of CV-PDT can be overcome by using crystal violet (CV) in combination with the membrane-active photosensitizer, Merocyanine 540 (MC540). When used under conditions that preserved an adequate fraction of normal human granulocyte/macrophage progenitors (CFU-GM), CV-PDT failed to achieve meaningful reductions of DU145 prostate, H69 small cell lung cancer, and MDA-MB-435S breast cancer cells. Melphalan-resistant L1210/L-PAM1, adriamycin-resistant P388/ADR, and adriamycin-resistant HL-60/ADR leukemia cells were markedly less sensitive to CV-PDT than their wild-type counterparts, whereas cisplatin-resistant H69/CDDP cells were more sensitive than wild-type H69 cells. Sequential exposure to MC540- and CV-PDT under conditions that preserved an adequate fraction (73% and 29%, respectively) of normal CD34-positive hematopoietic stem cells and granulocyte/macrophage progenitors was highly effective against H69 (99.997% reduction) and H69/CDDP (99.999% reduction) cells, but ineffective against HL-60/ADR, MDA-MB-435S, and DU145 cells. CV thus shows only limited promise as a single-modality purging agent. However, in certain situations, clinically meaningful tumor cell depletions can be obtained by using CV in combination with a second photosensitizer such as MC540. 相似文献
68.
Generalised diffusion processes are discussed using the theory of stochastic processes and several elementary results are proved for the survival probability of a pair of particles with an arbitrary potential. The reaction probability conditioned on reaction ultimately occurring is considered and its backward equation is determined. In the case of the Coulomb potential the probability is shown analytically to be identical in both the attractive and repulsive cases for a given absolute value of rc. The utility of this result in numerical solutions of the Debye—Smoluchowski equation is discussed. 相似文献
69.
Nmr and UV studies show that -dimethylamino--bromostyrene, I, undergoes SNl reaction in H2O and HClO4 (kSNl = 6 × 10?1sec.?1 at 25°). The vinyl cation has an extraordinary selectivity for capture by aromatic amines relative to H2O, including I itself to give the dimer II. 相似文献
70.
Oleg A. Raitman Andrei B. Kharitonov Maya Zayats Eugenii Katz Itamar Willner 《Analytica chimica acta》2004,504(1):101-111
Crosslinked films consisting of the acrylamide-acrylamidophenylboronic acid copolymer that are imprinted with recognition sites for β-nicotinamide adenine dinucleotide (NAD+), β-nicotinamide adenine dinucleotide phosphate NADP+, and their reduced forms (NAD(P)H), are assembled on Au-coated glass supports. The binding of the oxidized cofactors NAD+ or NADP+ or the reduced cofactors NADH or NADPH to the respective imprinted sites results in the swelling of the polymer films through the uptake of water. Surface plasmon resonance (SPR) spectroscopy is employed to follow the binding of the different cofactors to the respective imprinted sites. The imprinted recognition sites reveal selectivity towards the association of the imprinted cofactors. The method enables the analysis of the NAD(P)+ and NAD(P)H cofactors in the concentration range of 1×10−6 to 1×10−3 M. The cofactor-imprinted films associated with the Au-coated glass supports act as active interfaces for the characterization of biocatalyzed transformations that involve the cofactor-dependent enzymes. This is exemplified with the characterization of the biocatalyzed oxidation of lactate to pyruvate in the presence of NAD+ and lactate dehydrogenase using the NADH-imprinted polymer film. 相似文献