全文获取类型
收费全文 | 9577篇 |
免费 | 255篇 |
国内免费 | 37篇 |
专业分类
化学 | 4769篇 |
晶体学 | 213篇 |
力学 | 334篇 |
数学 | 934篇 |
物理学 | 2248篇 |
无线电 | 1371篇 |
出版年
2023年 | 82篇 |
2022年 | 173篇 |
2021年 | 186篇 |
2020年 | 236篇 |
2019年 | 228篇 |
2018年 | 178篇 |
2017年 | 177篇 |
2016年 | 262篇 |
2015年 | 214篇 |
2014年 | 304篇 |
2013年 | 677篇 |
2012年 | 492篇 |
2011年 | 554篇 |
2010年 | 328篇 |
2009年 | 329篇 |
2008年 | 459篇 |
2007年 | 446篇 |
2006年 | 354篇 |
2005年 | 325篇 |
2004年 | 260篇 |
2003年 | 194篇 |
2002年 | 183篇 |
2001年 | 133篇 |
2000年 | 115篇 |
1999年 | 90篇 |
1998年 | 87篇 |
1997年 | 70篇 |
1996年 | 92篇 |
1995年 | 93篇 |
1994年 | 105篇 |
1993年 | 124篇 |
1992年 | 113篇 |
1991年 | 79篇 |
1990年 | 87篇 |
1989年 | 81篇 |
1988年 | 96篇 |
1987年 | 90篇 |
1986年 | 74篇 |
1985年 | 142篇 |
1984年 | 149篇 |
1983年 | 122篇 |
1982年 | 105篇 |
1981年 | 104篇 |
1980年 | 106篇 |
1979年 | 106篇 |
1978年 | 105篇 |
1977年 | 91篇 |
1976年 | 87篇 |
1974年 | 75篇 |
1973年 | 82篇 |
排序方式: 共有9869条查询结果,搜索用时 0 毫秒
1.
The serine protease, DegP exhibits proteolytic and chaperone activities, essential for cellular protein quality control and normal cell development in eukaryotes. The P. falciparum DegP is essential for the parasite survival and required to combat the oscillating thermal stress conditions during the infection, protein quality checks and protein homeostasis in the extra-cytoplasmic compartments, thereby establishing it as a potential target for drug development against malaria. Previous studies have shown that diisopropyl fluorophosphate (DFP) and the peptide SPMFKGV inhibit E. coli DegP protease activity. To identify novel potential inhibitors specific to PfDegP allosteric and the catalytic binding sites, we performed a high throughput in silico screening using Malaria Box, Pathogen Box, Maybridge library, ChEMBL library and the library of FDA approved compounds. The screening helped identify five best binders that showed high affinity to PfDegP allosteric (T0873, T2823, T2801, , CD00811) and the catalytic binding site (T0078L, T1524, T2328, BTB11534 and 552691). Further, molecular dynamics simulation analysis revealed RJC02337, BTB11534 as the best hits forming a stable complex. WaterMap and electrostatic complementarity were used to evaluate the novel bio-isosteric chemotypes of RJC02337, that led to the identification of 231 chemotypes that exhibited better binding affinity. Further analysis of the top 5 chemotypes, based on better binding affinity, revealed that the addition of electron donors like nitrogen and sulphur to the side chains of butanoate group are more favoured than the backbone of butanoate group. In a nutshell, the present study helps identify novel, potent and Plasmodium specific inhibitors, using high throughput in silico screening and bio-isosteric replacement, which may be experimentally validated. RJC02337相似文献
2.
This paper addresses the problem of power control in a multihop wireless network supporting multicast traffic. We face the problem of forwarding packet traffic to multicast group members while meeting constraints on the signal-to-interference-plus-noise ratio (SINR) at the intended receivers. First, we present a distributed algorithm which, given the set of multicast senders and their corresponding receivers, provides an optimal solution when it exists, which minimizes the total transmit power. When no optimal solution can be found for the given set of multicast senders and receivers, we introduce a distributed, joint scheduling and power control algorithm which eliminates the weak connections and tries to maximize the number of successful multicast transmissions. The algorithm allows the other senders to solve the power control problem and minimize the total transmit power. We show that our distributed algorithm converges to the optimal solution when it exists, and performs close to centralized, heuristic algorithms that have been proposed to address the joint scheduling and power control problem. 相似文献
3.
4.
A new family of annulated inositols (inosito-inositols) has been conceptualized. Naphthalene has been elaborated into novel cyclohexa-annulated neo- and chiro-inositols, with two additional hydroxyl functionalities, through a series of stereoselective oxyfunctionalization protocols. The trans-ring fusion present in these new annulated inositols ensures conformational locking. 相似文献
5.
Europium (Eu+) ions were confined in a Paul trap and detected by non-destructive method. Storage time of Eu+ ions achieved in vacuum was improved by orders of magnitude employing buffer gas cooling. The experimentally detected signal
was fitted to the ion response signal and the total number of ions trapped was estimated. It is found that the peak signal
amplitude as well as the product of FWHM and the peak signal amplitude is proportional to the total number of trapped ions.
The trapped ion secular frequency was swept at different rates and its effect on the absorption line profile was studied both
experimentally and theoretically. 相似文献
6.
A Monte Carlo simulation method is used to study thermal desorption of gas molecules from mixed adlayers containing two species. The effects of lateral interactions among adatoms and initial surface coverage on the desorption spectra are examined. It is shown that attractive lateral interactions lead to sharper peaks and that desorption occurs at high temperatures, whereas repulsive interactions lead to multiple peak spectra. It is found that interactions between unlike molecules affect the spectra for species with lower desorption energy only, and that the two species desorb together only in certain cases. Lateral interactions also affect the desorption kinetics significantly and very different behavior for the two species may be obtained. 相似文献
7.
Gupta R. Hero A.O. III 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(8):1951-1969
We investigate high-rate quantization for various detection and reconstruction loss criteria. A new distortion measure is introduced which accounts for global loss in best attainable binary hypothesis testing performance. The distortion criterion is related to the area under the receiver-operating-characteristic (ROC) curve. Specifically, motivated by Sanov's theorem, we define a performance curve as the trajectory of the pair of optimal asymptotic Type I and Type II error rates of the most powerful Neyman-Pearson test of the hypotheses. The distortion measure is then defined as the difference between the area-under-the-curve (AUC) of the optimal pre-encoded hypothesis test and the AUC of the optimal post-encoded hypothesis test. As compared to many previously introduced distortion measures for decision making, this distortion measure has the advantage of being independent of any detection thresholds or priors on the hypotheses, which are generally difficult to specify in the code design process. A high-resolution Zador-Gersho type of analysis is applied to characterize the point density and the inertial profile associated with the optimal high-rate vector quantizer. The analysis applies to a restricted class of high-rate quantizers that have bounded cells with vanishing volumes. The optimal point density is used to specify a Lloyd-type algorithm which allocates its finest resolution to regions where the gradient of the pre-encoded likelihood ratio has greatest magnitude. 相似文献
8.
M.K. Gupta Vijay Gupta Manoj Kumar 《Journal of Mathematical Analysis and Applications》2007,330(2):799-816
In the present paper we introduce a new family of linear positive operators and study some direct and inverse results in simultaneous approximation. 相似文献
9.
In this paper, we suggest and analyze a new two-step predictor–corrector type iterative method free from second derivatives for solving nonlinear equations of the type f(x)=0. This new method includes the two-step Newton method as a special case. We prove that the new iterative method is of fourth-order. Several examples are given to illustrate the efficiency of this new method and its comparison with other iterative methods. This method can be considered as a significant improvement of the Newton method and its variant forms. 相似文献
10.
A tutorial review of a classic paper by Samuel J. Mason (1954) is described. That paper contained the first definition of a unilateral power gain for a linear two-port and the first proof that this grain is invariant with respect to linear lossless reciprocal four-port embeddings, thereby making it useful as a figure of merit intrinsic to the device. In this work, that original paper is brought up to date, a tutorial exposition of its contents is presented in a modern form, and its significance and applications in microwave engineering are discussed. The subsequent advances in the subject area are summarized, so that the original paper can be placed within a broader context and understood with a more general perspective 相似文献