全文获取类型
收费全文 | 9109篇 |
免费 | 1170篇 |
国内免费 | 1302篇 |
专业分类
化学 | 5552篇 |
晶体学 | 85篇 |
力学 | 1351篇 |
综合类 | 65篇 |
数学 | 518篇 |
物理学 | 4010篇 |
出版年
2024年 | 23篇 |
2023年 | 111篇 |
2022年 | 257篇 |
2021年 | 273篇 |
2020年 | 368篇 |
2019年 | 313篇 |
2018年 | 292篇 |
2017年 | 374篇 |
2016年 | 386篇 |
2015年 | 364篇 |
2014年 | 475篇 |
2013年 | 737篇 |
2012年 | 587篇 |
2011年 | 637篇 |
2010年 | 483篇 |
2009年 | 548篇 |
2008年 | 509篇 |
2007年 | 561篇 |
2006年 | 474篇 |
2005年 | 494篇 |
2004年 | 418篇 |
2003年 | 349篇 |
2002年 | 311篇 |
2001年 | 309篇 |
2000年 | 246篇 |
1999年 | 224篇 |
1998年 | 200篇 |
1997年 | 165篇 |
1996年 | 150篇 |
1995年 | 148篇 |
1994年 | 121篇 |
1993年 | 89篇 |
1992年 | 78篇 |
1991年 | 71篇 |
1990年 | 64篇 |
1989年 | 41篇 |
1988年 | 46篇 |
1987年 | 33篇 |
1986年 | 30篇 |
1985年 | 31篇 |
1984年 | 31篇 |
1983年 | 11篇 |
1982年 | 25篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1979年 | 19篇 |
1978年 | 10篇 |
1977年 | 22篇 |
1976年 | 13篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
291.
The main techniques developed to characterize chitosan are recalled. The interaction of chitosan with oppositely charged surfactants was investigated giving very important surface activity effects. A few chemical modifications are described and the new properties obtained are mentioned: alkylation gives amphiphilic polymers having interesting thickening behavior; grafting cyclodextrin (chit‐CD) gives a polymer able to include hydrophobic molecules; grafting adamantane gives an amphiphilic polymer able to specifically interact with chit‐CD forming a temporary network with gel‐like behavior.
292.
The present study investigated the modification of mesoscale inhomogeneous distribu-tion of soil wetness, resulting from mesoscale irrigation over arid or semiarid lands in mid-latitude in the later summer or early autumn, on mesoscale climate under conditions withand without synoptic flow influence, using an interactive model between soil and atmo-sphere. The simulations indicated that after a mesoscale irrgation, a wet soil breeze circu-lation was thermally forced, which was, in many features, similar to that of the sea breezecirculation. The influence of synoptic flows on the structure of thermally--induced wet soilbreeze circulation was also discussed. 相似文献
293.
Conditions were found, under which an anomalous relationship should be observed in the energies of sequential ionization of molecules ("anomalous" molecules) such that a subsequent potential (In+1) is less than the preceding potential (In). These conditions are a function of the electronic vibrational instability of molecules or their ions upon change in the number of electrons in the system. An interrelationship was found with the previously proposed concept of effective electron—electron attraction in molecular systems.Institute of Physiologically Active Compounds, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 738–741, March, 1992. 相似文献
294.
R. Winkler J. Wilhelm M. Capitelli C. Gorse 《Plasma Chemistry and Plasma Processing》1992,12(1):71-87
Calculations of the electron energy distribution and of relevant macroscopic quantities of collision-dominated, weakly ionized plasmas under rf field action have been performed with increasing degrees of ionization, and the impact of the electron-electron interaction on these quantities was determined. The investigations were performed for the gas plasmas in CO and H2 as representatives of molecular plasmas The energy distribution and macroscopic quantities are obtained by solving the nonstationary Bolizmann equation for a given rf field and degree of ionization taking into accoung and additional Fokker-Planck term besides the collision integrals for the elastic and the main inelastic collision processes. In these molecular plasmas a remarkable impact of the electron-electron interaction connected with increasing Maxwellization is observed for degrees of ionization greater than 10. 相似文献
295.
Biman Bagchi 《Journal of Chemical Sciences》1987,99(4):243-252
The canonical average of the Boltzmann factor of the interaction potential, as measured by a test particle, is shown to be
equal to the inverse of the fraction of the average number
of 1-particle Mayer clusters. The potential distribution theory is used to derive an analytic expression for a mean number
of small clusters
1≤n<N, in anN-particle system) in the mean-field expression. Near the spinodal density, the average number of small clusters undergo a
sharp change. Computation of pressure shows that only the first four clusters produce surprisingly good agreement with known
pressure even beyond the spinodal density.
Contribution No. 439 from the Solid State and Structural Chemistry Unit 相似文献
296.
F. E. Regnier 《Chromatographia》1987,24(1):241-251
Summary During the past decade, HPLC has developed into a powerful new technique for the analysis of complex mixtures of biological
macromolecules. Through the use of microparticulate supports of vastly improved mechanican strength, superior stationary phase
chemistry, and advanced instrumentation, it is now possible to separate biological macromolecules more than 10 times faster
and with greater resolution than in the classical SEC, IEC, HIC, bioaffinity, and hydroxyapetite chromatography columns. Additionally,
the introduction of new separation modes such as RPC and metal chelate make it possible to carry out separations that were
not possible with the classical gel-type media. It is anticipated that 1) expanded use of non-porous media, 2) development
of new stationary phases for carbohydrates, 3) greater throughput and resolution in preparative separations, and 4) better
understanding of retention mechanisms are a few of the areas of macromolecular separations in which advances can be expected
in the next few years. 相似文献
297.
The solubilities of o-, m- and p-xylene in water were measured at 25.0°C up to 250, 385, and 50 MPa, respectively. The solubility increased with increasing pressure up to 120 MPa (50 MPa for p-xylene) and then decreased. The reaction volumes, Vo accompanying the dissolution at 0.1 MPa were estimated as –3.6±0.5, –3.4±0.5, and –4.1±0.5 cm3-mol–1 for o-, m-, and p-xylene, respectively, from the pressure dependences of the solubilities. The limiting partial molar volumes, of p- and o-xylene in water under high pressure were estimated from Vo and the molar volume of the xylene. The partial molar volumes decreased with increasing pressure. The reaction volume for the formation of intra-molecular pairwise hydrophobic interaction between the methyl groups, as proposed by Ben-Naim, is discussed for the Vo of p- and o-xylene at 0.1 MPa. 相似文献
298.
299.
Sai Manoj N. V. T. Gorantla Harsha S. Karnamkkott Selvakumar Arumugam Sangita Mondal Kartik Chandra Mondal 《Journal of computational chemistry》2023,44(1):43-60
The factors/structural features which are responsible for the binding, activation and reduction of N2 to NH3 by FeMoco of nitrogenase have not been completely understood well. Several relevant model complexes by Holland et al. and Peters et al. have been synthesized, characterized and studied by theoretical calculations. For a matter of fact, those complexes are much different than real active N2-binding Fe-sites of FeMoco, which possesses a central C(4-) ion having an eight valence electrons as an μ6-bridge. Here, a series of [(S3C(0))Fe(II/I/0)-N2]n- complexes in different charged/spin states containing a coordinated σ- and π-donor C(0)-atom which possesses eight outer shell electrons [carbone, (Ph3P)2C(0); Ph3P→C(0)←PPh3] and three S-donor sites (i.e. -S-Ar), have been studied by DFT, QTAIM, and EDA-NOCV calculations. The effect of the weak field ligand on Fe-centres and the subsequent N2-binding has been studied by EDA-NOCV analysis. The role of the oxidation state of Fe and N2-binding in different charged and spin states of the complex have been investigated by EDA-NOCV analyses. The intrinsic interaction energies of the Fe−N2 bond are in the range from −42/−35 to −67 kcal/mol in their corresponding ground states. The S3C(0) donor set is argued here to be closer to the actual coordination environment of one of the six Fe-centres of nitrogenase. In comparison, the captivating model complexes reported by Holland et al. and Peter et al. possess a stronger π-acceptor C-ring (S2Cring donor, π-C donor) and stronger donor set like CP3 (σ-C donor) ligands, respectively. 相似文献
300.
利用ALD制备了TiO2限域的Pd催化剂, 研究了限域空间内Pd纳米颗粒与TiO2的界面作用对1,4-丁炔二醇(BYD)加氢性能的影响. 相比于管外负载型催化剂, 限域催化剂在催化1,4-丁炔二醇选择性加氢反应中体现出非常高的催化活性和1,4-丁烯二醇的选择性. HR-TEM、 EDX-Mapping、 XRD、 XPS和H2-TPR表征说明, 限域体系中Pd-TiO2的界面相互作用强于传统TiO2表面负载型Pd催化剂, 这种强界面作用不仅能够提高BYD的加氢活性, 也可抑制半加氢产物1,4-丁烯二醇的异构化和深度加氢, 提高1,4-丁烯二醇的选择性, 而且限域结构也可阻止管内壁Pd纳米颗粒的脱落, 提高催化剂的稳定性. 相似文献