全文获取类型
收费全文 | 36515篇 |
免费 | 5215篇 |
国内免费 | 5098篇 |
专业分类
化学 | 26924篇 |
晶体学 | 587篇 |
力学 | 2014篇 |
综合类 | 517篇 |
数学 | 4671篇 |
物理学 | 12115篇 |
出版年
2024年 | 67篇 |
2023年 | 528篇 |
2022年 | 1012篇 |
2021年 | 1030篇 |
2020年 | 1152篇 |
2019年 | 1167篇 |
2018年 | 1043篇 |
2017年 | 1050篇 |
2016年 | 1450篇 |
2015年 | 1514篇 |
2014年 | 1850篇 |
2013年 | 2517篇 |
2012年 | 2909篇 |
2011年 | 3119篇 |
2010年 | 2349篇 |
2009年 | 2351篇 |
2008年 | 2551篇 |
2007年 | 2324篇 |
2006年 | 2137篇 |
2005年 | 1884篇 |
2004年 | 1522篇 |
2003年 | 1243篇 |
2002年 | 1326篇 |
2001年 | 1189篇 |
2000年 | 944篇 |
1999年 | 799篇 |
1998年 | 662篇 |
1997年 | 533篇 |
1996年 | 554篇 |
1995年 | 464篇 |
1994年 | 449篇 |
1993年 | 408篇 |
1992年 | 383篇 |
1991年 | 331篇 |
1990年 | 278篇 |
1989年 | 229篇 |
1988年 | 203篇 |
1987年 | 156篇 |
1986年 | 163篇 |
1985年 | 176篇 |
1984年 | 122篇 |
1983年 | 75篇 |
1982年 | 80篇 |
1981年 | 61篇 |
1980年 | 60篇 |
1979年 | 70篇 |
1978年 | 42篇 |
1976年 | 37篇 |
1974年 | 41篇 |
1973年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Lin Zhengyan 《数学年刊B辑(英文版)》1998,19(3):281-292
§1.IntroductionandResultsLet{Xn,n1}beasequenceofrandomvariableswithacommondistributionfunctionF(x)andletXn1Xn2…Xnnbetheor... 相似文献
152.
LetK be a compact Hausdorff space, and letT be an irreducible Markov operator onC(K). We show that ifgεC(K) satisfies sup
N
‖Σ
j
=0N
T
j
g‖<∞, then (and only then) there existsfεC(K) with (I − T)f=g. Generalizing the result to irreducible Markov operator representations of certain semi-groups, we obtain that bounded cocycles
are (continuous) coboundaries. For minimal semi-group actions inC(K), no restriction on the semi-group is needed. 相似文献
153.
154.
155.
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
156.
157.
该文讨论局部可分度量空间闭s映象的分解定理, 证明了正则的Fréchet空间是局部可分度量空间的闭s映象当且仅当满足如下条件: 具有点可数的cs*网, 第一可数的闭子空间是局部可分的, 且Lindelof的闭子空间是可分的. 相似文献
158.
Li Lin 《Annals of Differential Equations》2007,23(4):433-439
In this paper,we study some permanence and global stability to a nonau- tonomous nonlinear discrete single species system,and obtain some sufficient condition of global stability to the system. 相似文献
159.
利用球磨法制备石墨-六角氮化硼微晶混合物,并在6.1 GPa、800~1 500 ℃条件下与水进行高压反应,以便研究用水作触媒合成B-C-N三元化合物的可能性。通过对反应产物的XRD、XPS谱分析发现:高压下随着温度的升高,反应产物中出现再结晶石墨,其晶化程度逐渐提高;但没有出现再结晶六角氮化硼,也未出现立方氮化硼。在球磨不充分条件下,石墨-六角氮化硼混合物的XRD谱没有完全弥散,它们与水高压反应时,能观察到石墨与立方氮化硼分别结晶的现象,但都没有形成B-C-N晶化结构。 相似文献
160.
Xiao‐Hui Liu Yan‐Guo Li Ying Lin Yue‐Sheng Li 《Journal of polymer science. Part A, Polymer chemistry》2007,45(7):1272-1281
The reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylonitrile (AN) mediated by 2‐cyanoprop‐2‐yl dithiobenzoate was first applied to synthesize polyacrylonitrile (PAN) with a high molecular weight up to 32,800 and a polydispersity index as low as 1.29. The key to success was ascribed to the optimization of the experimental conditions to increase the fragmentation reaction efficiency of the intermediate radical. In accordance with the atom transfer radical polymerization of AN, ethylene carbonate was also a better solvent candidate for providing higher controlled/living RAFT polymerization behaviors than dimethylformamide and dimethyl sulfoxide. The various experimental parameters, including the temperature, the molar ratio of dithiobenzoate to the initiator, the molar ratio of the monomer to dithiobenzoate, the monomer concentration, and the addition of the comonomer, were varied to improve the control of the molecular weight and polydispersity index. The molecular weights of PANs were validated by gel permeation chromatography along with a universal calibration procedure and intrinsic viscosity measurements. 1H NMR analysis confirmed the high chain‐end functionality of the resultant polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1272–1281, 2007 相似文献