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   141190篇
  免费   21121篇
  国内免费   16044篇
化学   75497篇
晶体学   1228篇
力学   6109篇
综合类   748篇
数学   13391篇
物理学   40202篇
无线电   41180篇
  2024年   364篇
  2023年   3256篇
  2022年   3858篇
  2021年   5255篇
  2020年   5469篇
  2019年   4927篇
  2018年   4579篇
  2017年   4317篇
  2016年   6087篇
  2015年   6432篇
  2014年   7817篇
  2013年   10104篇
  2012年   11893篇
  2011年   12283篇
  2010年   9104篇
  2009年   9043篇
  2008年   9299篇
  2007年   8427篇
  2006年   7952篇
  2005年   6949篇
  2004年   5087篇
  2003年   4249篇
  2002年   3831篇
  2001年   3280篇
  2000年   2940篇
  1999年   3077篇
  1998年   2616篇
  1997年   2271篇
  1996年   2235篇
  1995年   1985篇
  1994年   1695篇
  1993年   1381篇
  1992年   1214篇
  1991年   1039篇
  1990年   869篇
  1989年   616篇
  1988年   479篇
  1987年   394篇
  1986年   394篇
  1985年   303篇
  1984年   222篇
  1983年   194篇
  1982年   146篇
  1981年   90篇
  1980年   69篇
  1979年   26篇
  1978年   30篇
  1976年   24篇
  1975年   23篇
  1957年   29篇
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
101.
Guo  Yan  Li  Zhuang  Wei  Yuxi  Zhang  Xinxu  Shi  Kexin 《Journal of Solid State Electrochemistry》2022,26(4):1051-1065
Journal of Solid State Electrochemistry - Polyvinylpyrrolidone (PVP) and graphene (G)-modified iron oxides (Fe2O3-PVP-G) are prepared by a simple hydrothermal reaction. Their morphology and...  相似文献   
102.
103.
Crystallography Reports - A cobalt coordination polymer, {[Co(L1)2(H2O)2] · (HCOO)2 · H2O}n, where L1 is a bis(4-(1H-imidazol-1-yl)phenyl)methanone, has been synthesized and characterized...  相似文献   
104.
The Ramanujan Journal - Inspired by Andrews and Merca’s recent work on the number of even parts over all partitions into distinct parts, we introduce a new kind of Beck type identities, which...  相似文献   
105.
106.
Let L be an additive map between (real or complex) matrix algebras sending n×n Hermitian idempotent matrices to m×m Hermitian idempotent matrices. We show that there are nonnegative integers p,q with n(p+q)=rm and an m×m unitary matrix U such thatL(A)=U[(Ip?A)(Iq?At)0m?r]U?,for any n×n Hermitian A with rational trace. We also extend this result to the (complex) von Neumann algebra setting, and provide a supplement to the Dye-Bunce-Wright Theorem asserting that every additive map of Hermitian idempotents extends to a Jordan ?-homomorphism.  相似文献   
107.
Bromine-based flow batteries (Br-FBs) are considered one of the most promising energy storage systems due to their features of high energy density and low cost. However, they generally suffer from uncontrolled diffusion of corrosive bromine particularly at high temperatures. That is because the interaction between polybromide anions and the commonly used complexing agent (N–methyl–N–ethyl–pyrrolidinium bromide [MEP]) decreases with increasing temperatures, which causes serious self-discharge and capacity fade. Herein, a novel bromine complexing agent, 1–ethyl–2–methyl–pyridinium bromide (BCA), is introduced in Br-FBs to solve the above problems. It is proven that BCA can combine with polybromide anions very well even at a high temperature of 60 °C. Moreover, the BCA contributes to decreasing the electrochemical polarization of Br/Br2 couple, which in turn improves their power density. As a result, a zinc–bromine flow battery with BCA as the complexing agent can achieve a high energy efficiency of 84% at 40 mA cm−2, even at high temperature of 60 °C and it can stably run for more than 400 cycles without obvious performance decay. This paper provides an effective complexing agent to enable a wide temperature range Br-FB.  相似文献   
108.
Methodology and Computing in Applied Probability - This paper is devoted to the study of an optimal investment and risk control problem for an insurer. The risky asset process and the insurance...  相似文献   
109.
Electromagnetic signal emitted by satellite communication (satcom) transmitters are used to identify specific individual uplink satcom terminals sharing the common transponder in real environment, which is known as specific emitter identification (SEI) that allows for early indications and warning (I&W) of the targets carrying satcom furnishment and furthermore the real time electromagnetic situation awareness in military operations. In this paper, the authors are the first to propose the identification of specific transmitters of satcom by using probabilistic neural networks (PNN) to reach the goal of target recognition. We have been devoted to the examination by exploring the feasibility of utilizing the Hilbert transform to signal preprocessing, applying the discrete wavelet transform to feature extraction, and employing the PNN to perform the classification of stationary signals. There are a total of 1000 sampling time series with binary phase shift keying (BPSK) modulation originated by five types of satcom transmitters in the test. The established PNNs classifier implements the data testing and finally yields satisfactory accuracy at 8 dB(±1 dB) carrier to noise ratio, which indicates the feasibility of our method, and even the keen insight of its application in military.  相似文献   
110.
Cancer remains an intractable medical problem. Rapid diagnosis and identification of cancer are critical to differentiate it from nonmalignant diseases. High-throughput biofluid metabolic analysis has potential for cancer diagnosis. Nevertheless, the present metabolite analysis method does not meet the demand for high-throughput screening of diseases. Herein, a high-throughput, cost-effective, and noninvasive urine metabolic profiling method based on TiO2/MXene-assisted laser desorption/ionization mass spectrometry (LDI-MS) is presented for the efficient screening of bladder cancer (BC) and nonmalignant urinary disease. Combined with machine learning, TiO2/MXene-assisted LDI-MS enables high diagnostic accuracy (96.8%) for the classification of patient groups (including 47 BC and 46 ureteral calculus (UC) patients) from healthy controls (113 cases). In addition, BC patients can also be identified from noncancerous UC individuals with an accuracy of 88.3% in the independent test cohort. Furthermore, metabolite variations between BC and UC individuals are investigated based on relative quantification, and related pathways are also discussed. These results suggest that this method, based on urine metabolic patterns, provides a potential tool for rapidly distinguishing urinary diseases and it may pave the way for precision medicine.  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