全文获取类型
收费全文 | 35650篇 |
免费 | 3661篇 |
国内免费 | 1314篇 |
专业分类
化学 | 3103篇 |
晶体学 | 43篇 |
力学 | 1040篇 |
综合类 | 322篇 |
数学 | 8928篇 |
物理学 | 4724篇 |
无线电 | 22465篇 |
出版年
2024年 | 142篇 |
2023年 | 577篇 |
2022年 | 1049篇 |
2021年 | 1257篇 |
2020年 | 1248篇 |
2019年 | 824篇 |
2018年 | 770篇 |
2017年 | 1115篇 |
2016年 | 1282篇 |
2015年 | 1291篇 |
2014年 | 2324篇 |
2013年 | 2319篇 |
2012年 | 2324篇 |
2011年 | 2260篇 |
2010年 | 1840篇 |
2009年 | 1881篇 |
2008年 | 2138篇 |
2007年 | 2063篇 |
2006年 | 1899篇 |
2005年 | 1642篇 |
2004年 | 1400篇 |
2003年 | 1502篇 |
2002年 | 1176篇 |
2001年 | 988篇 |
2000年 | 940篇 |
1999年 | 750篇 |
1998年 | 594篇 |
1997年 | 564篇 |
1996年 | 442篇 |
1995年 | 366篇 |
1994年 | 292篇 |
1993年 | 220篇 |
1992年 | 154篇 |
1991年 | 120篇 |
1990年 | 115篇 |
1989年 | 87篇 |
1988年 | 81篇 |
1987年 | 48篇 |
1986年 | 60篇 |
1985年 | 68篇 |
1984年 | 71篇 |
1983年 | 22篇 |
1982年 | 43篇 |
1981年 | 42篇 |
1980年 | 36篇 |
1979年 | 30篇 |
1978年 | 31篇 |
1977年 | 43篇 |
1976年 | 25篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Indrajit Lahiri 《Journal of Mathematical Analysis and Applications》2002,271(1):206-216
In this paper we prove a uniqueness theorem for meromorphic functions sharing three values with some weight which improves some known results. 相似文献
102.
Toward Fuzzy Optimization without Mathematical Ambiguity 总被引:15,自引:0,他引:15
Baoding Liu 《Fuzzy Optimization and Decision Making》2002,1(1):43-63
Fuzzy programming has been discussed widely in literature and applied in such various disciplines as operations research, economic management, business administration, and engineering. The main purpose of this paper is to present a brief review on fuzzy programming models, and classify them into three broad classes: expected value model, chance-constrained programming and dependent-chance programming. In order to solve general fuzzy programming models, a hybrid intelligent algorithm is also documented. Finally, some related topics are discussed. 相似文献
103.
104.
激光二极管反馈干涉的实验观测 总被引:7,自引:2,他引:5
利用LabView软件虚拟示波器和信号源,观测了激光二极管反馈干涉实验现象.实验证明反馈回激光二极管的光的入射方向和入射光强以及信号处理电路的带宽,对反馈干涉信号有很大的影响. 相似文献
105.
Dalila B. M. M. Fontes Eleni Hadjiconstantinou Nicos Christofides 《Journal of Global Optimization》2006,34(1):97-125
In this paper we obtain Lower Bounds (LBs) to concave cost network flow problems. The LBs are derived from state space relaxations
of a dynamic programming formulation, which involve the use of non-injective mapping functions guaranteing a reduction on
the cardinality of the state space. The general state space relaxation procedure is extended to address problems involving
transitions that go across several stages, as is the case of network flow problems. Applications for these LBs include: estimation
of the quality of heuristic solutions; local search methods that use information of the LB solution structure to find initial
solutions to restart the search (Fontes et al., 2003, Networks, 41, 221–228); and branch-and-bound (BB) methods having as
a bounding procedure a modified version of the LB algorithm developed here, (see Fontes et al., 2005a). These LBs are iteratively
improved by penalizing, in a Lagrangian fashion, customers not exactly satisfied or by performing state space modifications.
Both the penalties and the state space are updated by using the subgradient method. Additional constraints are developed to
improve further the LBs by reducing the searchable space. The computational results provided show that very good bounds can
be obtained for concave cost network flow problems, particularly for fixed-charge problems. 相似文献
106.
Given a principal value convolution on the Heisenberg group Hn = Cn×R, we study the relation between its Laguerre expansion and the Fourier-Bessel expansion of its limit on Cn. We also calculate the Dirichlet kernel for the Laguerre expansion on the group Hn. 相似文献
107.
宽带建设低潮期实际上是一次优胜劣汰的过程,宽带运营竞争的手段将由低价竞争转向服务质量和特色的竞争。应在重视宽带接入建设的同时,也要重视业务运营管理平台的建设。应从长远考虑,不应仅为了节省投资而降低对设备的要求。由于降低成本的主要方向是在线缆部分,因此EVDSL技术应用的速度将大大超过人们的预期。在网络建设上,IPDSLAM虽有优势但也有不足,还需要进一步的成熟、稳定和实践的检验。 相似文献
108.
Yu-Soo Lee Hyun-Ju Chung Jong-Han Joung Eung-Jo Kim Hee-Je Kim 《Optics & Laser Technology》2004,36(1):461-61
We describe the pulse forming of pulsed CO2 laser using multi-pulse superposition technique. Various pulse shapes, high duty cycle pulse forming network (PFN) are constructed by time sequence. This study shows a technology that makes it possible to make various long pulse shapes by activating SCRs of three PFN modules consecutively at a desirable delay time with the aid of a PIC one-chip microprocessor. The power supply for this experiment consists of three PFN modules. Each PFN module uses a capacitor, a pulse forming inductor, a SCR, a high voltage pulse transformer, and a bridge rectifier on each transformer secondary. The PFN modules operate at low voltage by driving the primary of HV pulse transformer. The secondary of the transformer has a full-wave rectifier, which passes the pulse energy to the load in a continuous sequence.We investigated various long pulse shapes as different trigger time intervals of SCRs among three PFN modules. As a result, we could obtain laser beam with various pulse shapes and durations from about 250 to 1000 μs. 相似文献
109.
In asynchronous transfer mode (ATM) networks, fixed length cells of 53 bytes are transmitted. A cell may be discarded during transmission due to buffer overflow or a detection of errors. Cell discarding seriously degrades transmission quality. The quality degradation can be reduced by employing efficient forward error control (FEC) to recover discarded cells. In this paper, we present the design and implementation of decoding equipment for FEC in ATM networks based on a single parity check (SPC) product code using very‐large‐scale integration (VLSI) technology. FEC allows the destination to reconstruct missing data cells by using redundant parity cells that the source adds to each block of data cells. The functionality of the design has been tested using the Model Sim 5.7cXE Simulation Package. The design has been implemented for a 5 ° 5 matrix of data cells in a Virtex‐E XCV 3200E FG1156 device. The simulation and synthesis results show that the decoding function can be completed in 81 clock cycles with an optimum clock of 56.8 MHz. A test bench was written to study the performance of the decoder, and the results are presented. 相似文献
110.
基于双因子认证技术的网络身份识别 总被引:5,自引:0,他引:5
本文提出了一种基于动态双因子认证技术的网络身份识别方法,用户每次登录的口令是利用系统时间和用户ID通过MD5加密算法计算得到,其通过MD5加密后生成的登录口令是随机的,这将进一步提高开放网络环境下身份识别的可靠性和安全性。同时,本文还提出网络身份识别技术可以应用到各类网站的服务器上,用来完成对用户身份的识别,以提高网络系统的安全性。 相似文献