首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1086篇
  免费   9篇
  国内免费   12篇
化学   595篇
晶体学   5篇
力学   35篇
数学   331篇
物理学   141篇
  2019年   6篇
  2016年   11篇
  2015年   13篇
  2014年   18篇
  2013年   31篇
  2012年   24篇
  2011年   37篇
  2010年   20篇
  2009年   23篇
  2008年   39篇
  2007年   50篇
  2006年   35篇
  2005年   41篇
  2004年   39篇
  2003年   26篇
  2002年   25篇
  2001年   23篇
  2000年   15篇
  1999年   12篇
  1998年   19篇
  1997年   12篇
  1996年   13篇
  1995年   21篇
  1994年   19篇
  1993年   11篇
  1992年   19篇
  1991年   15篇
  1990年   12篇
  1989年   15篇
  1988年   20篇
  1987年   21篇
  1986年   33篇
  1985年   27篇
  1984年   16篇
  1983年   11篇
  1982年   19篇
  1981年   16篇
  1980年   29篇
  1979年   31篇
  1978年   22篇
  1977年   10篇
  1976年   19篇
  1975年   19篇
  1974年   27篇
  1973年   20篇
  1972年   15篇
  1971年   14篇
  1970年   13篇
  1969年   6篇
  1968年   8篇
排序方式: 共有1107条查询结果,搜索用时 31 毫秒
51.
52.
53.
A series of samples of polystyrene (PS) –polyethylene (PE) interpenetrating polymer network (IPN)–like system was prepared by synthesis in situ. The measurement of uniaxial compression modulus of the IPN samples was used for the determination of mean molar mass of the polymer chain between two junction points of the polymer network – M̌C. The electron microscopic records gave an evidence about two phase structure of the IPN samples. Generally, the crystalline part of PE network in all IPN investigated samples is relatively low. The influence of the concentration of crosslinking agent on mechanical behaviour of the IPN samples was studied.  相似文献   
54.
55.
The mechanism of RAMAN scattering depends on molecular polarizability changes and therefore this method is especially useful for the study of non-polar bonds. This is shown by reviewing some analytical applications. Knowledge on polymer structure was especially promoted by studies of the lowest-frequency bending modes, of correlation splittings in case of crystallinity, and by measurements on depolarization of the laser light. RAMAN spectroscopy has possibilities for in-situ and multi-method measurements. Newer developments serving the polymer sciences are surface enhanced RAMAN scattering and the RAMAN spectroscopy of electroconducting polymers.  相似文献   
56.
The nicotinic acetylcholine receptor (nAcChR) of the electric organ of Torpedo californica fish exhibits a pronounced hysteresis loop in the high affinity binding of the neurotransmitter acetylcholine (AcCh). When increasing amounts of AcCh are added (pulse mode) an extremely long-lived, metastable conformer distribution is obtained (lower hysteresis branch) between low affinity AcCh binding states (Rl) and high (Rh) and very high (Rvh) affinity states. Dialysis conditions always lead to the equilibrium binding curve (upper hysteresis branch; K̄A = 5 × 10−9M, 4°C; one A bound to the R-monomer of Mr ≈ 290 000). Cyclic, pulse mode addition and dilution of AcCh results in scanning loops within the main hysteresis. The kinetic analysis of the changes in free and bound AcCh during the open-system conditions of dialysis, that releases the metastability, shows that the AcCh (A) binding proceeds along an induced-fit pathway according to A+Rh ⇋ ARn ⇋ ARvh. The rate constant of the step ARh → ARvh is k2 = 6 × 10−3s−1 and that of the reverse step is k−2 = 3 × 10−4s−1. Direct binding of A to free Rvh can be excluded. Therefore, the state Rvh does not preexist, it is induced and only stable, as ARvh, by bound AcCh. The metastability can be described in terms of long-lived ARvh ·R1 hybrid dimers. Physiologically, the metastable hybrid may be viewed as a saving device: the functionally important, channel-active R1 conformer is, at low AcCh-concentrations [A] < 1μM, prevented to convert to the desensitized states Rh and ARvh. Furtheron, AcCh enhances the phosphorylation of phosphatidyl inositol and the auto-phosphorylation of the receptor. If the AcCh binding hysteresis causes a phosphorylation hysteresis the desensitized nAcChR may serve as a memory molecule of the transsynaptic information signalling of the neurotransmission.  相似文献   
57.
58.
Neutron imaging as a method for non-destructive studies takes advantage of the alternative contrast mechanism of neutrons compared to X-rays: most of the light elements feature high contrast, whereas heavy elements are relatively transparent to neutrons. In the previous decade, the neutron imaging technique has made substantial progress in well-tailored and well-equipped beam lines, in improvements of the image recording quality and efficiency by new and modern imaging techniques, and in modern image processing tools.  相似文献   
59.
60.
Summary In the theory of functional analytic comparison of statistical experiments (started by L. LeCam) one can characterize equivalence classes of experiments by conical measures (in the sense of G. Choquet). We begin with a short proof of the (known) fact that any conical measure with normed resultant belongs to an experiment class. Then we are concerned with the special case of dominated experiments which are characterized by the extendability of their conical measures to finite concrete measures. These results are in close connection with a paper of E.N. Torgersen (Mixtures and products of dominated experiments. Ann. Statist. 5, 44–64 (1977)).After this we study class properties of experiments which are expressible in terms of their conical measures. Simple examples are domination, existence of bounded densities and compactness. It follows the investigation of a more profound class property which we call extremality and which generalizes the concept of an experiment with a sufficient and boundedly complete subalgebra. Finally we prove that the extreme points of the compact convex set of conical measures with normed resultant are just the conical measures of the extremal experiments.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号