全文获取类型
收费全文 | 24594篇 |
免费 | 777篇 |
国内免费 | 137篇 |
专业分类
化学 | 16323篇 |
晶体学 | 251篇 |
力学 | 725篇 |
综合类 | 1篇 |
数学 | 2289篇 |
物理学 | 5919篇 |
出版年
2023年 | 149篇 |
2022年 | 432篇 |
2021年 | 587篇 |
2020年 | 440篇 |
2019年 | 452篇 |
2018年 | 403篇 |
2017年 | 379篇 |
2016年 | 713篇 |
2015年 | 614篇 |
2014年 | 849篇 |
2013年 | 1485篇 |
2012年 | 1790篇 |
2011年 | 1987篇 |
2010年 | 1264篇 |
2009年 | 1082篇 |
2008年 | 1659篇 |
2007年 | 1448篇 |
2006年 | 1477篇 |
2005年 | 1261篇 |
2004年 | 1112篇 |
2003年 | 937篇 |
2002年 | 893篇 |
2001年 | 543篇 |
2000年 | 491篇 |
1999年 | 341篇 |
1998年 | 216篇 |
1997年 | 212篇 |
1996年 | 277篇 |
1995年 | 191篇 |
1994年 | 204篇 |
1993年 | 203篇 |
1992年 | 154篇 |
1991年 | 128篇 |
1990年 | 127篇 |
1989年 | 105篇 |
1988年 | 68篇 |
1987年 | 76篇 |
1986年 | 51篇 |
1985年 | 77篇 |
1984年 | 53篇 |
1983年 | 44篇 |
1982年 | 65篇 |
1981年 | 62篇 |
1979年 | 47篇 |
1978年 | 45篇 |
1977年 | 34篇 |
1976年 | 41篇 |
1975年 | 37篇 |
1974年 | 36篇 |
1973年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Alam MS Katayama N Kim IJ Li WC Lou XC Sun CR Bortoletto D Goldberg M Horwitz N Mestayer MD Moneti GC Sharma V Shipsey IP Skwarnicki T Csorna SE Letson T Brock IC Ferguson T Artuso M Bebek C Berkelman K Blucher E Byrd J Cassel DG Cheu E Coffman DM Crawford G DeSalvo R DeWire JW Drell PS Ehrlich R Galik RS Gittelman B Gray SW Halling AM Hartill DL Heltsley BK Kandaswamy J Kowalewski R Kreinick DL Kubota Y Lewis JD Mistry NB Mueller J Namjoshi R Nandi S Nordberg E O'Grady C Peterson D Pisharody M 《Physical review D: Particles and fields》1989,40(11):3790
102.
Dong Han Kim 《Journal of heterocyclic chemistry》1976,13(2):179-194
Acetic anhydride has been used widely in synthetic organic chemistry, especially in syntheses and transformations of heterocyclic compounds. These utilities are reviewed under the following classification. 相似文献
103.
Summary Real hypersurfaces of an almost Hermitian manifold naturally admit an almost contact metric structure and the (f, g, u, v, w, , , )-structure is defined on submanifolds of codimension 3 of an almost Hermitian manifold. We study the so-called semi-invariant submanifolds of a complex space form with almost contact metric compound structure which is a general notion of (f, g, u, v, w, , , )-structure.Dedicated to professor Eulyong Pak on his 60th birthdayThis research was partially supported by Korean Science and Engineering Foundation Grant. 相似文献
104.
Fabrication of hollow palladium spheres and their successful application to the recyclable heterogeneous catalyst for suzuki coupling reactions 总被引:25,自引:0,他引:25
Novel palladium hollow spheres were synthesized using silica spheres as a template, and they were successfully applied as recyclable heterogeneous catalysts for Suzuki cross coupling reactions. 相似文献
105.
Arthur A. Santilli Dong Han Kim Stephen V. Wanser 《Journal of heterocyclic chemistry》1972,9(2):309-313
Eighteen novel pyrimido[4,5-e][1,4]oxazepin-5-ones were prepared directly via the reaction of either ethyl 4-chloro-2-phenyl-5-pyrimidinecarboxylate (Ia) or ethyl 4-chloro-2-m-chlorophenyl-5-pyrimidinecarboxylate (Ib) with a variety of substituted 2-(alkylamino)ethanols. A typical example was the preparation of 8,9-dihydro-9-methyl-2-phenylpyrimido[4,5-e][1,4]-oxazepin-5(7H)-one (IIa) from the reaction of Ia with 2-(methylamino)ethanol. Hydrolytic cleavage of the lactone ring in IIa with sodium hydroxide solution, followed by acidification with hydrochloric acid afforded 4-[(2-hydroxyethyl)methylamino]-2-phenyl-5-pyrimidinecarboxylic acid (IV). Reactions of IIa with concentrated ammonium hydroxide or hydrazine also caused cleavage of the lactone ring, giving the corresponding amide (V) or hydrazide (VI), respectively. Structural assignments were supported by infrared and nuclear magnetic resonance spectra. 相似文献
106.
The theory presented earlier [J. Kim and T. Keyes, Phys. Rev. E 66, 051110 (2002)] is analyzed to determine the information available from the two-dimensional Raman spectrum R((5))(t(2),t(1)) in liquids. The known spectra are well represented by the sum of two products of ordinary time correlations predicted by the theory. The shape of R((5)) is related in general to the values of simple same-time averages and concepts amenable to physical intuition. Using standard models for the time correlations entering the theory, specific analytic expressions for the spectrum are obtained depending on two parameters and a time scale, and the behavior of the spectrum is mapped out in the parameter space. 相似文献
107.
A tandem free radical cyclization-rearrangement sequence was designed and executed to produce tricyclo[4.3.2.0(1,5)]undecane 7 from cyclopentene 6A in a single operation. The total synthesis of suberosenone was accomplished from 7. 相似文献
108.
Homologous recombination (HR) repair deficiency impairs the proper maintenance of genomic stability, thus rendering cancer cells vulnerable to loss or inhibition of DNA repair proteins, such as poly(ADP-ribose) polymerase-1 (PARP-1). Inhibitors of nuclear PARPs are effective therapeutics for a number of different types of cancers. Here we review key concepts and current progress on the therapeutic use of PARP inhibitors (PARPi). PARPi selectively induce synthetic lethality in cancer cells with homologous recombination deficiencies (HRDs), the most notable being cancer cells harboring mutations in the BRCA1 and BRCA2 genes. Recent clinical evidence, however, shows that PARPi can be effective as cancer therapeutics regardless of BRCA1/2 or HRD status, suggesting that a broader population of patients might benefit from PARPi therapy. Currently, four PARPi have been approved by the Food and Drug Administration (FDA) for the treatment of advanced ovarian and breast cancer with deleterious BRCA mutations. Although PARPi have been shown to improve progression-free survival, cancer cells inevitably develop resistance, which poses a significant obstacle to the prolonged use of PARP inhibitors. For example, somatic BRCA1/2 reversion mutations are often identified in patients with BRCA1/2-mutated cancers after treatment with platinum-based therapy, causing restoration of HR capacity and thus conferring PARPi resistance. Accordingly, PARPi have been studied in combination with other targeted therapies to overcome PARPi resistance, enhance PARPi efficacy, and sensitize tumors to PARP inhibition. Moreover, multiple clinical trials are now actively underway to evaluate novel combinations of PARPi with other anticancer therapies for the treatment of PARPi-resistant cancer. In this review, we highlight the mechanisms of action of PARP inhibitors with or without BRCA1/2 defects and provide an overview of the ongoing clinical trials of PARPi. We also review the current progress on PARPi-based combination strategies and PARP inhibitor resistance.Subject terms: Cancer therapy, Mechanisms of disease, PolyADP-ribosylation 相似文献
109.
The intramolecular Diels-Alder (IMDA) reactions of C(8)-substituted decatrienoates have been studied. The stereospecific formation of 11 via an endo-boat-9 transition state attests to the powerful directing influence of a C(8) substituent in the IMDA of decatrienoate. In addition, the contrasting observations that stereospecific 9 --> 11 occurs at room temperature while the nor-tert-butyl substrate (4a) requires 125 degrees C/5 h reaction conditions and produces a 60:40 mixture of diastereomers provide clear evidence that a bulky C(8) substituent is a powerful conformational activator of the IMDA. 相似文献
110.
Jin R Jureller JE Kim HY Scherer NF 《Journal of the American Chemical Society》2005,127(36):12482-12483
Femtosecond laser excited second harmonic (SH) activity from single Ag nanoparticles is reported. A correlation of SH single-particle measurements with high-resolution imaging of particle morphology by TEM was achieved by creating position markers on an optical and electron transparent substrate (Si3N4 thin film, approximately 100 nm). We compared the SH activity of single Ag nanoparticles (nanospheres versus nanorods) and cluster structures (composed of two or multiple particles, e.g., dimers and trimers). The direct correlation of single-particle structures and SH activity, spectral and power dependence, strongly suggests one-photon resonant driven nonlinear oscillator response mechanism. 相似文献