全文获取类型
收费全文 | 25109篇 |
免费 | 654篇 |
国内免费 | 154篇 |
专业分类
化学 | 16700篇 |
晶体学 | 123篇 |
力学 | 575篇 |
数学 | 4334篇 |
物理学 | 3434篇 |
综合类 | 751篇 |
出版年
2022年 | 179篇 |
2021年 | 260篇 |
2020年 | 302篇 |
2019年 | 317篇 |
2018年 | 233篇 |
2017年 | 195篇 |
2016年 | 482篇 |
2015年 | 457篇 |
2014年 | 494篇 |
2013年 | 1306篇 |
2012年 | 1208篇 |
2011年 | 1510篇 |
2010年 | 743篇 |
2009年 | 707篇 |
2008年 | 1323篇 |
2007年 | 1345篇 |
2006年 | 1313篇 |
2005年 | 1310篇 |
2004年 | 1135篇 |
2003年 | 984篇 |
2002年 | 892篇 |
2001年 | 354篇 |
2000年 | 282篇 |
1999年 | 249篇 |
1998年 | 276篇 |
1997年 | 307篇 |
1996年 | 359篇 |
1995年 | 241篇 |
1994年 | 280篇 |
1993年 | 263篇 |
1992年 | 237篇 |
1991年 | 240篇 |
1990年 | 191篇 |
1989年 | 231篇 |
1988年 | 237篇 |
1987年 | 201篇 |
1986年 | 196篇 |
1985年 | 295篇 |
1984年 | 337篇 |
1983年 | 219篇 |
1982年 | 367篇 |
1981年 | 336篇 |
1980年 | 316篇 |
1979年 | 317篇 |
1978年 | 324篇 |
1977年 | 292篇 |
1976年 | 281篇 |
1975年 | 250篇 |
1974年 | 248篇 |
1973年 | 234篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
Rupert L. Frank Ari Laptev Elliott H. Lieb Robert Seiringer 《Letters in Mathematical Physics》2006,77(3):309-316
Inequalities are derived for power sums of the real part and the modulus of the eigenvalues of a Schrödinger operator with a complex-valued potential. 相似文献
122.
123.
Robert J. Willis Stephen B. Huxford 《The Journal of the Operational Research Society》1991,42(9):727-731
A complex manual rostering system for directory assistance, telephone operators has been rationalized and the technique of integer programming used to automatically generate staff rosters. These rosters can be generated by relatively unskilled clerical staff. They result in operator costs comparable to manually generated rosters and can be produced in a fraction of the time taken to produce their manual counterparts. Implementation is reported. 相似文献
124.
Béatrice Bussery-Honvault Robert Moszynski Joël Boissoles 《Journal of Molecular Spectroscopy》2005,232(1):73-79
Symmetry-adapted perturbation theory has been applied to compute the He-CH3F potential with the CH3F molecule assumed rigid. The potential has a global minimum of −48.9 cm−1 at the center of mass separation of 7.2 bohr with the helium atom lying along the C-F bond on the hydrogen’s side. The computed points were fitted to an analytic energy surface with a correct asymptotic behaviour. This potential has been used to compute the pressure broadening (PB) coefficients for the (j, k) = (0, 0) → (1, 0) and (1, 0) → (2, 0) rotational transitions of CH3F perturbed by helium for a wide range of temperatures. Close-coupling results are compared with the experimental data of Willey et al. [J. Chem. Phys. 97 (1992) 4723], Beaky et al. [J. Mol. Struct. 352/353 (1995) 245] and infinite order sudden results are compared with those of Grigoriev et al. [J. Mol. Struct. 186 (1997) 48] for the ν6 band of CH3F perturbed by helium at room temperature. To our knowledge, present work is the first attempt of making fully ab initio calculations of collisional cross-sections and pressure broadening coefficients for this simple symmetric top system at low and room temperature. 相似文献
125.
126.
Kikue S. Burnham Robert Roth Faith Zhou Wenya Fan Emma Brouk Mehari Stifanos 《Journal of polymer science. Part A, Polymer chemistry》2006,44(24):6909-6925
In an attempt to develop a low‐k interlayer dielectric, adamantane‐diphenyldiethynyl moiety containing oligomer is prepared. Oligomerization of 1,3,5,7‐tetrakis[3/4‐ethynylphenyl]adamantane ( 4 ) is accomplished by a Glaser–Hay oxidative coupling with 1,3,5‐triethynylbenzene and phenylacetylene end‐capping agent. The CHCl3 soluble oligomer is then thermally treated by step‐curing at 200, 300, 380, and 450 °C for 30 min at each temperature under nitrogen flow to render a shiny void‐free black polymer. TGA analysis indicates that the polymer is stable under nitrogen up to 500 °C with a marginal decomposition up to 800 °C. Solid‐state 13C NMR, Raman scattering, and FTIR are used to characterize the structure of the polymer. The polymer consists of amorphous carbon networks with the adamantane moieties and nanosized graphitic regions (clusters), which are generated from the thermal crosslinking of the diphenyldiethynyl units. It shows a remarkably low linear coefficient of thermal expansion (~25 ppm/°C), presumably due to the presence of the disordered graphitic structure. Its high density (~1.21 g/cm3), refractive index (~1.80 at 632 nm), and Young's modulus (~17.0 GPa) are also consistent with the interpretation. This study reveals important details about the effect of microscopic structure on the macroscopic properties of the highly crosslinked polymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6909–6925, 2006 相似文献
127.
Gerald W. Evans Robert Fairbairn 《The Journal of the Operational Research Society》1989,40(11):971-981
A 0-1 integer linear programme for the selection and scheduling of US National Aeronautics and Space Administration (NASA) missions over a long planning horizon is presented. This model was formulated to allow a higher-level user-interaction with an advanced missions database currently being developed. The model implicitly considers the multi-objective nature of the problem, which results from the desire to maximize benefits in several categories as well as from the desire to minimize cost. In addition, the model allows the planner much flexibility in the selection process. This is accomplished by allowing the planner the ability to specify long- or short-term budget constraints, precursor/follow-on mission requirements, or any number of other idiosyncratic constraints which might be of importance in the decision process. Small example problems are solved in order to illustrate the approach, and areas for further research are discussed. 相似文献
128.
Monika Schuster Robert Inführ Claudia Turecek Jürgen Stampfl Franz Varga Robert Liska 《Monatshefte für Chemie / Chemical Monthly》2006,4(4):843-853
To substitute cross-linked photopolymers in rapid prototyping of mold materials and therefore extend the range of materials
which can be casted, organo-soluble photopolymers were developed. Branched bisalkylacrylamides were suitable as base component
for such formulations, due to their high reactivity, good mechanical properties, and excellent solubility of the formed polymers.
These molding materials were used to prepare cellular biocompatible materials which could be used as bone replacement materials.
Biocompatible crosslinkers based on methacrylates from hydrolyzed gelatine or lactic acid ethyleneglycol blockcopolymers and
commercially available reactive diluents are the base components of such a formulation. Biocompatibility was investigated
by osteoblast-like cells. Cellular biocompatible parts were obtained by thermal polymerization in soluble mould materials
prepared by 3D-photoshaping. 相似文献
129.
Wolfgang H. Binder Laura Petraru Robert Sachenshofer Ronald Zirbs 《Monatshefte für Chemie / Chemical Monthly》2006,137(7):835-841
Summary. The surface modification of nanoparticles via azide/alkine-1,3-dipolar cycloaddition-reactions is described. Ligand exchange onto various nanoparticles was monitored by
1H NMR spectroscopy and formed the basis for the attachment of ligands onto the nanoparticles and their subsequent modification
by dipolar cycloaddition reactions. Nanoparticle-surfaces were monitored by binding onto self-assembled monolayers derivatized
with matching supramolecular interactions after derivatization. 相似文献
130.
Robert W. Baddeley Cheryl E. Praeger Csaba Schneider 《Transactions of the American Mathematical Society》2006,358(4):1619-1641
A permutation group is innately transitive if it has a transitive minimal normal subgroup, which is referred to as a plinth. We study the class of finite, innately transitive permutation groups that can be embedded into wreath products in product action. This investigation is carried out by observing that such a wreath product preserves a natural Cartesian decomposition of the underlying set. Previously we classified the possible embeddings in the case where the plinth is simple. Here we extend that classification and identify several different types of Cartesian decompositions that can be preserved by an innately transitive group with a non-abelian plinth. These different types of decompositions lead to different types of embeddings of the acting group into wreath products in product action. We also obtain a full characterisation of embeddings of innately transitive groups with diagonal type into such wreath products.