全文获取类型
收费全文 | 33211篇 |
免费 | 2847篇 |
国内免费 | 3043篇 |
专业分类
化学 | 7446篇 |
晶体学 | 192篇 |
力学 | 2852篇 |
综合类 | 294篇 |
数学 | 7100篇 |
物理学 | 5302篇 |
综合类 | 15915篇 |
出版年
2024年 | 131篇 |
2023年 | 333篇 |
2022年 | 633篇 |
2021年 | 745篇 |
2020年 | 826篇 |
2019年 | 744篇 |
2018年 | 750篇 |
2017年 | 935篇 |
2016年 | 1124篇 |
2015年 | 966篇 |
2014年 | 1582篇 |
2013年 | 2133篇 |
2012年 | 1846篇 |
2011年 | 1921篇 |
2010年 | 1529篇 |
2009年 | 1807篇 |
2008年 | 1855篇 |
2007年 | 2226篇 |
2006年 | 1916篇 |
2005年 | 1695篇 |
2004年 | 1567篇 |
2003年 | 1364篇 |
2002年 | 1323篇 |
2001年 | 1108篇 |
2000年 | 1001篇 |
1999年 | 973篇 |
1998年 | 799篇 |
1997年 | 725篇 |
1996年 | 619篇 |
1995年 | 601篇 |
1994年 | 541篇 |
1993年 | 498篇 |
1992年 | 405篇 |
1991年 | 387篇 |
1990年 | 296篇 |
1989年 | 269篇 |
1988年 | 222篇 |
1987年 | 170篇 |
1986年 | 114篇 |
1985年 | 87篇 |
1984年 | 58篇 |
1983年 | 31篇 |
1982年 | 55篇 |
1981年 | 35篇 |
1980年 | 42篇 |
1979年 | 27篇 |
1978年 | 15篇 |
1977年 | 19篇 |
1976年 | 18篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Summary The dependence of the chloride distribution coefficient on the co-ion of solutions of different alkali fluorides, MF, up to 11M is tested on the strongly basic anion-exchange resin AG1-X10. Under the same experimental conditions the distribution coefficient decreases in the following order for M+: Na+>K+>Rb+>Cs+. This can be explained by the different co-ion-chloride interactions. The consequence of this interaction for a chromatographic separation of chloride is shown with 5M KF and CsF solutions, used as eluants. Depending on the fluoride concentration, the distribution coefficient passes through a minimum value to increase again at higher electrolyte concentration. The non-exchange electrolyte in the resin phase is responsible for this effect. In addition, the bromide and the iodide distribution coefficients up to 10M KF solutions are determined. One results is that the selectivity coefficient between halide ions increases at higher electrolyte concentrations. 相似文献
72.
Hiltrud Breitenfelder-Manske Friedrich Kohler 《Monatshefte für Chemie / Chemical Monthly》1985,116(11):1247-1261
The second virial coefficients of homonuclear three-centerLennard-Jones molecules are calculated with various parameters of the isosceles triangle connecting the three sites. A special effort is made to establish the reducedBoyle temperaturesT
B and the values of the second virial coefficients atT/T
B=0.3 for the sake of comparison with one- and two-centerLennard-Jones molecules. It is shown that it is possible to find parameter values of the interaction potential of one- and two-centerLennard-Jones molecules which give very similar values of second virial coefficients forT/T
B0.3, and the equivalence conditions are established. These conditions might not only give a basis for a microscopic scaling of state variables, but also some restrictions for the validity of the group contribution concept.Presented in part at the DFG-Colloquium at Paderborn, 19th April 1982, and at the 5th Conference on Mixtures of Nonelectrolytes and Intermolecular Interactions, April 18–22, 1983, at Halle (GDR). 相似文献
73.
Rabindra N. Roy James J. Gibbons Guilio LaCross Jr. Charles W. Krueger 《Journal of solution chemistry》1976,5(5):333-343
The two thermodynamic dissociation constants of glycine at 11 temperatures from 5 to 55°C in 50 mass % methanol-water mixed solvent have been determined from precise emf measurements with hydrogen-silver bromide electrodes in cells without liquid junction. The first acidic dissociation constant (K
1)for the process HG+H++G± is expressed as a function ofT(oK) by the equation pK
1 = 2043.5/T – 9.6504 + 0.019308T. At 25°C, pK
1is 2.961 in the mixed solvent, as compared with 2.350 in water, with H°=1497 cal-mole–1, G°=4038 cal-mole–1, S°=–8.52 cal-°K–1-mole–1, and C
p
o
=–53 cal-°K–1-mole–1. The second acidic dissociation constant (K
2)for the process G±H++G– over the temperature range studied is given by the equation pK
2 = 3627.1/T – 7.2371 + 0.015587T. At 25°C, pK
2is 9.578 in MeOH–H2O as compared with 9.780 in water, whereas H° is 10,257 cal-mole–1, G° is 13,063 cal-mole–1, S° is –9.41 cal-°K–1-mole–1, and C
p
o
is –43 cal-°K–1-mole–1. The protonated glycine becomes weaker in 50 mass % methanol-water, whereas the second dissociation process becomes stronger despite the lower dielectric constant of the mixed solvent (=56.3 at 25°C). 相似文献
74.
Silyleneisthesimilarityofsilicontocarbene,and,likecarbeneinorganicreactions,itplaysaveryimportantroleinorganosiliconreactions.Inrecentyears,therehavebeenmanyreportsonsilylenesinquantumchemicalresearches[1—3].Investigationonitsorganicreactionshowsthatreali… 相似文献
75.
The influence of the vapors ofn-amyl orn-decyl alcohol on the stability of single thin liquid films, single bubbles, and foam columns was determined. It was found that the presence of surfactant vapors lowered the stability of foams and single foam films. The mechanism of the destabilizing action of the surfactant vapors on wet, dynamic foams under dynamic conditions is discussed. It is shown that the destabilizing action of the surfactant vapors is a further indication that surface elasticity forces are the main factor determining stability of wet, dynamic foams. 相似文献
76.
C. Maes J. Devaux R. Legras I. W. Parsons 《Journal of polymer science. Part A, Polymer chemistry》1995,33(12):1943-1955
A monofunctional maleimide-ended model compound was synthesized and purified. The thermal curing of this compound was followed by size exclusion chromatography and the molecular masses of the oligomers formed during the curing reaction were determined by mass spectroscopy. It was found that high molecular mass species were not thermally stable. At high temperature and after enough time, a strong decrease in the polydispersity of the oligomers and a significantly preferential formation of trimer were observed. From 13C-NMR characterization, a five membered ring structure was found for the trimer, which explains the thermal stability of this species. © 1995 John Wiley & Sons, Inc. 相似文献
77.
H. J. Greenberg W. P. Pierskalla 《Journal of Optimization Theory and Applications》1975,16(5-6):409-428
The primary concern of this paper is to investigate stability conditions for the mathematical program: findx E
n that maximizesf(x):g
j(x)0 for somej J, wheref is a real scalarvalued function and eachg is a real vector-valued function of possibly infinite dimension. It should be noted that we allow, possibly infinitely many, disjunctive forms. In an earlier work, Evans and Gould established stability theorems wheng is a continuous finite-dimensional real-vector function andJ=1. It is pointed out that the results of this paper reduce to the Evans-Gould results under their assumptions. Furthermore, since we use a slightly more general definition of lower and upper semicontinuous point-to-set mappings, we can dispense with the continuity ofg (except in a few instances where it is implied by convexity assumptions). 相似文献
78.
Lotka-Volterra方程的全局指数稳定性 总被引:2,自引:0,他引:2
曾永福 《四川大学学报(自然科学版)》2005,42(1):38-40
研究一类具有时滞的Lotka-Volterra生物方程,证明该系统在一定条件下存在正的平衡态,并给出了正平衡态指数稳定的充分条件。 相似文献
79.
作者在全面地分析影响河道水温变化各种因素的基础上,根据大渡河流域实测资料所推荐的有关计算纵向离散系数的经验公式.确定了一种适宜于河道一维非恒定流水温的预测模型.作者运用此模型预测了水库下泄低温水、火电厂温排水对下游水环境的影响及其应用价值,其结果可为制定水库生态用水调度方案和流域开发的环境影响评价提供科学依据. 相似文献
80.
在三轴试验基础上提出采用归纳定义方法来确定孔隙压力关系方程,其结论与根据弹性力学理论推导的结论是一致的,并指出了弹性力学理论推导过程中存在的不严密之处和理论适应性问题. 相似文献