全文获取类型
收费全文 | 440665篇 |
免费 | 20549篇 |
国内免费 | 11075篇 |
专业分类
化学 | 237662篇 |
晶体学 | 6633篇 |
力学 | 22907篇 |
综合类 | 543篇 |
数学 | 51212篇 |
物理学 | 153332篇 |
出版年
2022年 | 6024篇 |
2021年 | 7209篇 |
2020年 | 7576篇 |
2019年 | 7917篇 |
2018年 | 8806篇 |
2017年 | 8780篇 |
2016年 | 12621篇 |
2015年 | 9122篇 |
2014年 | 13110篇 |
2013年 | 23914篇 |
2012年 | 21953篇 |
2011年 | 24831篇 |
2010年 | 17686篇 |
2009年 | 17305篇 |
2008年 | 19986篇 |
2007年 | 19390篇 |
2006年 | 17876篇 |
2005年 | 15258篇 |
2004年 | 13395篇 |
2003年 | 11488篇 |
2002年 | 11240篇 |
2001年 | 12642篇 |
2000年 | 9634篇 |
1999年 | 8226篇 |
1998年 | 6940篇 |
1997年 | 6663篇 |
1996年 | 6475篇 |
1995年 | 5465篇 |
1994年 | 5380篇 |
1993年 | 4960篇 |
1992年 | 5257篇 |
1991年 | 5355篇 |
1990年 | 4958篇 |
1989年 | 4628篇 |
1988年 | 4294篇 |
1987年 | 4332篇 |
1986年 | 4101篇 |
1985年 | 4987篇 |
1984年 | 4950篇 |
1983年 | 4051篇 |
1982年 | 4118篇 |
1981年 | 3819篇 |
1980年 | 3731篇 |
1979年 | 3966篇 |
1978年 | 3944篇 |
1977年 | 3946篇 |
1976年 | 3929篇 |
1975年 | 3724篇 |
1974年 | 3663篇 |
1973年 | 3687篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
For two types of qutrits specified by the dynamical symmetry SU(3) and SU(2), we consider the difference in entanglement caused by the lack of quantum observables in the latter case. In particular, we show that the SU(2) qutrits can have specific separable entanglement caused by quantum correlations of intrinsic degrees of freedom in a single party without interparty correlations. 相似文献
202.
The following areal objects are considered: an ether thread contracting two material points and a multidimensional ether fibre in the pseudo-Euclidean world of events. An ether space-time model with an arbitrarily determined Riemannian metric is constructed and the problem of the λ term in Einstein equations is discussed in this regard. 相似文献
203.
Ke Sha Dongshuang Li Yapeng Li Xiaotian Liu Shuwei Wang Jingqi Guan Jingyuan Wang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5037-5049
Amphiphilic diblock copolymer polycaprolactone‐block‐poly(glycidyl methacrylate) (PCL‐b‐PGMA) was synthesized via enzymatic ring‐opening polymerization (eROP) and atom transfer radical polymerization (ATRP). Methanol first initiated eROP of ?‐caprolactone (?‐CL) in the presence of biocatalyst Novozyme‐435 under anhydrous conditions. The resulting monohydroxyl‐terminated polycaprolactone (PCL–OH) was subsequently converted to a bromine‐ended macroinitiator (PCL–Br) for ATRP by esterification with α‐bromopropionyl bromide. PCL‐b‐PGMA diblock copolymers were synthesized in a subsequent ATRP of glycidyl methacrylate (GMA). A kinetic analysis of ATRP indicated a living/controlled radical process. The macromolecular structures were characterized for PCL–OH, PCL–Br, and the block copolymers by means of nuclear magnetic resonance, gel permeation chromatography, and infrared spectroscopy. Differential scanning calorimetry and wide‐angle X‐ray diffraction analyses indicated that the copolymer composition (?‐CL/GMA) had a great influence on the thermal properties. The well‐defined, amphiphilic diblock copolymer PCL‐b‐PGMA self‐assembled into nanoscale micelles in aqueous solutions, as investigated by dynamic light scattering and transmission electron microscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5037–5049, 2007 相似文献
204.
In this research, a simple, sensitive chemiluminescence (CL) method for the determination of humic acid (HA) in water samples was first developed based on the redox reaction between humic acid and cerium(IV) in the acidic condition. Different with the former redox CL reaction which occurred in alkaline solution, no enhancers were needed and neither precipitation nor a second contamination would occur in the present CL system. Comparing with other spectrometric methods, we find that the proposed analysis system had better applicability and accuracy. Under the optimal experiment conditions, the CL peak height was linear with the concentration of HA in the range of 0.03 to 10.0 microg mL(-1). The detection limit is 0.01 microg mL(-1) (S/N = 3), and the relative standard deviation was 2.3% for 0.5 microg mL(-1) HA solution with eleven repeated measurements. The present CL method was successfully applied to the determination of HA in tap water, spring water and river water samples with good recovery from 90.0 to 110.0%. A possible CL mechanism was proposed based on the results of UV and fluorescence spectrometry and the CL spectrum of HA. It was speculated that the semi-quinone radicals in the excited state were the emitters. 相似文献
205.
The supersymetric path integrals in solving the problem of relativistic spinning particle interacting with pseudoscalar potentials
is examined. The relative propagator is presented by means of path integral, where the spin degrees of freedom are described
by odd Grassmannian variables and the gauge invariant part of the effective action has a form similar to the standard pseudoclassical
action given by Berezin and Marinov. After integrating over fermionic variables (Grassmannian variables), the problem is reduced
to a nonrelativistic one with an effective supersymetric potential. Some explicit examples are considered, where we have extracted
the energy spectrum of the electron and the wave functions.
PACS numbers: 03.65. Ca-Formalism, 03.65. Db-Functional analytical methods, 03.65. Pm-Relativistic wave equations. 相似文献
206.
Zhitian Liu Lei Wang Junwu Chen Feng Wang Xiaoying Ouyang Yong Cao 《Journal of polymer science. Part A, Polymer chemistry》2007,45(5):756-767
2,5‐Bis(2‐bromofluorene‐7‐yl)silole was prepared by a modified one‐pot synthesis with a reverse addition procedure, from which novel silole‐containing polyfluorenes with binary random and alternating structures (silole contents between 4.5 and 25% and high Mw up to 509 kDa were successfully synthesized. The well‐defined repeating unit of the alternating copolymer comprises a terfluorene and a silole ring. Optoelectronic properties including UV absorption, electrochemistry, photoluminescence (PL), and electroluminescence (EL) of the copolymers were examined. The different excitation energy transfers from fluorene to silole of the copolymers in solution and in the solid state were compared. The films of the copolymers showed silole‐dominant green emissions with high absolute PL quantum yields up to 83%. EL devices of the copolymers with a configuration of ITO/PEDOT/copolymer/Ba/Al displayed exclusive silole emissions peaked at around 543 nm and the highest EL efficiency was achieved with the alternating copolymer. Using the alternating copolymer and poly(9,9‐dioctylfluorene) as the blend‐type emissive layer, a maximum external quantum efficiency of 1.99% (four times to that of the neat film) was realized, which was a high efficiency so far reported for silole‐containing polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 756–767, 2007 相似文献
207.
208.
L. S. Pul’kina 《Journal of Mathematical Sciences》2007,144(1):3832-3840
The author proves the existence and uniqueness of a generalized solution of a nonlocal problem with an integral condition
for a hyperbolic equation with n spatial variables.
This work is a continuation of the studies started in [3–5], where the solvability problem of nonlocal problems with an integral
condition was studied for hyperbolic equations on the plane.
__________
Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 33, Suzdal
Conference-2004, Part 1, 2005. 相似文献
209.
210.