全文获取类型
收费全文 | 6977篇 |
免费 | 1141篇 |
国内免费 | 732篇 |
专业分类
化学 | 4699篇 |
晶体学 | 72篇 |
力学 | 408篇 |
综合类 | 42篇 |
数学 | 645篇 |
物理学 | 2984篇 |
出版年
2024年 | 16篇 |
2023年 | 149篇 |
2022年 | 169篇 |
2021年 | 176篇 |
2020年 | 266篇 |
2019年 | 220篇 |
2018年 | 207篇 |
2017年 | 186篇 |
2016年 | 295篇 |
2015年 | 286篇 |
2014年 | 357篇 |
2013年 | 501篇 |
2012年 | 542篇 |
2011年 | 599篇 |
2010年 | 400篇 |
2009年 | 407篇 |
2008年 | 431篇 |
2007年 | 370篇 |
2006年 | 358篇 |
2005年 | 331篇 |
2004年 | 275篇 |
2003年 | 202篇 |
2002年 | 226篇 |
2001年 | 175篇 |
2000年 | 173篇 |
1999年 | 178篇 |
1998年 | 133篇 |
1997年 | 131篇 |
1996年 | 155篇 |
1995年 | 109篇 |
1994年 | 115篇 |
1993年 | 109篇 |
1992年 | 102篇 |
1991年 | 82篇 |
1990年 | 65篇 |
1989年 | 74篇 |
1988年 | 52篇 |
1987年 | 47篇 |
1986年 | 38篇 |
1985年 | 34篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1970年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有8850条查询结果,搜索用时 31 毫秒
951.
Hybrids of vinblastine and phomopsin, designed by a molecular modelling study, were elaborated in order to target tubulin. The key step of the synthesis (fragmentation and insertion of vindoline) was mediated by an internal N-carboxyanhydride (or O-acylcarbamate). This reaction was diastereospecific and addition of silver salts could reverse the diastereoselectivity. Even if the synthesized compounds are inactive, this synthesis represents an original example of a C-N fragmentation mediated by a N-carboxyanhydride. 相似文献
952.
Chen GJ Gao CY Tian JL Tang J Gu W Liu X Yan SP Liao DZ Cheng P 《Dalton transactions (Cambridge, England : 2003)》2011,40(20):5579-5583
By changing the ratio of reactants, two mononuclear Dy complexes, [Dy(phen)(acac)(3)] (1) and [Dy(phen)(2)(NO(3))(2)(acac)]·H(2)O (2) have been synthesized and structurally characterized. In 1, a Dy atom bearing square-antiprism coordination geometry exhibits SMM behaviour, while compound 2 with a bicapped-square-antiprism geometry does not show such SMM properties. The different magnetic behaviours seen in 1 and 2 are probably due to a different coordination environment and ligand field around the Dy(III) ions. The results proved the important influence of the structural environment of a SMM on its magnetic behaviour. 相似文献
953.
Lewis basic DABCO-functionalized 3D-like metal-organic framework, Zn-MOF, catalyzes nitroaldol (Henry) reaction of 4-nitrobenzaldehyde with nitroalkanes in a size-dependent manner. Small nitroalkanes give rise to higher conversion than larger ones. This MOF-based heterogeneous catalyst is very robust and can be recycled several times without losing its activity. 相似文献
954.
Gee MB Cox NR Jiao Y Bentenitis N Weeerasinghe S Smith PE 《Journal of chemical theory and computation》2011,7(5):1369-1380
A classical nonpolarizable force field is presented for the simulation of aqueous alkali halide solutions (MX), where M = Li(+), Na(+), K(+), Rb(+), Cs(+) and X = F(-), Cl(-), Br(-), I(-), and their interactions with biomolecules. The models are specifically designed to reproduce the experimental Kirkwood-Buff integrals, and thereby the solution salt activities, as a function of salt concentration. Additionally, we demonstrate that these models reasonably reproduce other experimental properties including ion diffusion constants, dielectric decrements, and the excess heats of mixing. The parameters are developed by considering the properties of aqueous NaX and MCl solutions using a previously established model for NaCl. Transferability of the parameters to other salts is then established by the successful simulation of additional aqueous salt solutions, KI and CsBr, not originally included in the parameterization procedure. 相似文献
955.
A sensitive, specific and rapid liquid chromatography-mass spectrometry (LC-MS/MS) method has been developed and validated for enantioselective determination of darusentan enantiomers, orally active potent endothelin-A receptor antagonist, in rat plasma. The plasma samples were pretreated by protein precipitation with methanol and baseline chromatographic separation was performed on a Chiralcel OD-RH column with a mobile phase consisting of acetonitrile/water/formic acid (50:50:0.1, v/v/v) at a flow rate of 0.5 mL/min. The detection was accomplished by multiple-reaction monitoring (MRM) scanning via electrospray ionization (ESI) source operating in the negative ionization mode. The calibration curve was linear over the investigated concentration from 0.500 to 2500 ng/mL (r≥0.995) for each enantiomer using 50 μL of rat plasma. The lower limit of quantitation (LLOQ) for each enantiomer was 0.500 ng/mL. The intra- and inter-day precisions were not more than 10.2% and the accuracy was within the range from -5.4 to 6.3% for darusentan enantiomers. No chiral inversion was observed during the plasma preparation, storage and analysis. The method proved adequate for enantioselective pharmacokinetic studies of darusentan enantiomers after oral administration of three different doses of racemic darusentan. 相似文献
956.
Min Gao Xiaolei Wang Ming Gu Zhiguo Su Ye Wang Jan‐Christer Janson 《Journal of separation science》2011,34(15):1853-1858
A porous polyamide resin is shown to possess hydrogen bond acceptor properties suitable for the separation of polyphenolic solutes such as phenolic acids, flavonols and flavonoids. The separation is achieved in the presence of solvent mixtures of acetic acid and ethanol. The extent of hydrogen bond adsorption is reviewed based on data obtained from the elution behaviour of a variety of simple polyphenolic solutes. Polyamide adsorption chromatography was applied for the purification of resveratrol and polydatin from Polygonum cuspidatum Sieb. & Zucc. 相似文献
957.
Cerruti CD Touboul D Guérineau V Petit VW Laprévote O Brunelle A 《Analytical and bioanalytical chemistry》2011,401(1):75-87
Mass spectrometry imaging of lipids using MALDI–TOF/TOF mass spectrometers is of growing interest for chemical mapping of
organic compounds at the surface of tissue sections. Many efforts have been devoted to the best matrix choice and deposition
technique. Nevertheless, the identification of lipid species desorbed from tissue sections remains problematic. It is now
well-known that protonated, sodium- and potassium-cationized lipids are detected from biological samples, thus complicating
the data analysis. A new sample preparation method is proposed, involving the use of lithium salts in the matrix solution
in order to simplify the mass spectra with only lithium-cationized molecules instead of a mixture of various cationized species.
Five different lithium salts were tested. Among them, lithium trifluoroacetate and lithium iodide merged the different lipid
adducts into one single lithium-cationized species. An optimized sample preparation protocol demonstrated that the lithium
trifluoroacetate salt slightly increased desorption of phosphatidylcholines. Mass spectrometry images acquired on rat brain
tissue sections by adding lithium trifluoroacetate showed the best results in terms of image contrast. Moreover, more structurally
relevant fragments were generated by tandem mass spectrometry when analyzing lithium-cationized species. 相似文献
958.
The function-valued Padé-type approximant (FPTA) was defined in the inner product space [8]. In this work, we choose the coefficients in the Neumann power series to make the inner product with both sides a function-valued system of equations to yield a scalar system. Then we express an FPTA in the determinant form. To avoid the direct computation of the determinants, we present the E-algorithm for FPTA based on the vector-valued E-algorithm given by Brezinski [4]. The method of FPTA via E-algorithm (FPTAVEA) not only includes all previous methods but overcomes their essential difficulties. The numerical experiment for a typical integral equation [1] illustrates that the method of FPTAVEA is simpler and more effective for obtaining the characteristic values and the characteristic functions than all previous methods. In addition, this method is also applicable to other Fredholm integral equations of the second kind without explicit characteristic values and characteristic functions. A corresponding example [12] is given and the numerical result is the same as that in [12]. 相似文献
959.
Ying-Qiu Gu 《Advances in Applied Clifford Algebras》2011,21(1):103-119
The special theory of relativity is the foundation of modern physics, but its unusual postulate of invariant vacuum speed
of light results in a number of plausible paradoxes. This situation leads to radical criticisms and suspicions against the
theory of relativity. In this paper, from the perspective that the relativity is nothing but a geometry, we give a uniform
resolution to some famous and typical paradoxes such as the ladder paradox, the Ehrenfest’s rotational disc paradox. The discussion
shows that all the paradoxes are caused by misinterpretation of concepts. We misused the global simultaneity and the principle
of relativity. As a geometry of Minkowski space-time, special relativity can never result in a logical contradiction. 相似文献
960.
The nonlinear buckling behavior of a 3D-braided composite cylindrical shell of finite length subjected to internal pressure
in thermal environments is considered. According to a new micromacromechanical model, a 3D-braided composite may be treated
as a cell system where the geometry of each cell strongly depends on its position in the cross section of the cylindrical
shell. The material properties of the epoxy matrix are expressed as linear functions of temperature. The governing equations
are based on Reddy’s higher-order shear deformation theory of shells with a von Karman–Donnell-type kinematic nonlinearity
and include thermal effects. The singular perturbation technique is employed to determine the buckling pressure and the postbuckling
equilibrium paths of the shell. 相似文献