全文获取类型
收费全文 | 1597篇 |
免费 | 52篇 |
国内免费 | 5篇 |
专业分类
化学 | 1058篇 |
晶体学 | 16篇 |
力学 | 36篇 |
数学 | 197篇 |
物理学 | 347篇 |
出版年
2023年 | 41篇 |
2022年 | 45篇 |
2021年 | 53篇 |
2020年 | 46篇 |
2019年 | 46篇 |
2018年 | 41篇 |
2017年 | 22篇 |
2016年 | 48篇 |
2015年 | 45篇 |
2014年 | 50篇 |
2013年 | 83篇 |
2012年 | 83篇 |
2011年 | 128篇 |
2010年 | 46篇 |
2009年 | 62篇 |
2008年 | 80篇 |
2007年 | 79篇 |
2006年 | 63篇 |
2005年 | 48篇 |
2004年 | 55篇 |
2003年 | 28篇 |
2002年 | 29篇 |
2001年 | 20篇 |
2000年 | 24篇 |
1999年 | 13篇 |
1998年 | 13篇 |
1997年 | 17篇 |
1996年 | 15篇 |
1995年 | 11篇 |
1994年 | 15篇 |
1993年 | 23篇 |
1992年 | 8篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 7篇 |
排序方式: 共有1654条查询结果,搜索用时 11 毫秒
61.
62.
P. R. J. Saey A. Ringbom T. W. Bowyer M. Zähringer M. Auer A. Faanhof C. Labuschagne M. S. Al-Rashidi U. Tippawan B. Verboomen 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(2):1133-1142
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) specifies that radioxenon measurements should be performed at 40 or more stations worldwide within the International Monitoring System (IMS). Measuring radioxenon is one of the principle techniques to detect underground nuclear explosions. Specifically, presence and ratios of different radioxenon isotopes allows determining whether a detection event under consideration originated from a nuclear explosion or a civilian source. However, radioxenon monitoring on a global scale is a novel technology and the global civil background must be characterized sufficiently. This paper lays out a study, based on several unique measurement campaigns, of the worldwide concentrations and sources of verification relevant xenon isotopes. It complements the experience already gathered with radioxenon measurements within the CTBT IMS programme and focuses on locations in Belgium, Germany, Kuwait, Thailand and South Africa where very little information was available on ambient xenon levels or interesting sites offered opportunities to learn more about emissions from known sources. The findings corroborate the hypothesis that a few major radioxenon sources contribute in great part to the global radioxenon background. Additionally, the existence of independent sources of 131mXe (the daughter of 131I) has been demonstrated, which has some potential to bias the isotopic signature of signals from nuclear explosions. 相似文献
63.
Lucas Lapatsanis 《Tetrahedron letters》1978,19(41):3943-3944
Various diphenylmethyl ethers are prepared under mild conditions by using tri-diphenylmethyl phosphate as alkylating agent. O-Diphenylmethyl-L(?)-Lactic Acid is prepared by this method. 相似文献
64.
Vivek B. Shah Gregory S. Orf Sean Reisch Lucas B. Harrington Mindy Prado Robert E. Blankenship Pratim Biswas 《Analytical and bioanalytical chemistry》2012,404(8):2329-2338
Photosynthetic organisms have light-harvesting complexes that absorb and transfer energy efficiently to reaction centers. Light-harvesting complexes (LHCs) have received increased attention in order to understand the natural photosynthetic process and also to utilize their unique properties in fabricating efficient artificial and bio-hybrid devices to capture solar energy. In this work, LHCs with different architectures, sizes, and absorption spectra, such as chlorosomes, Fenna–Matthews–Olson (FMO) protein, LH2 complex, and phycobilisome have been characterized by an electrospray-scanning mobility particle-sizer system (ES-SMPS). The size measured by ES-SMPS for FMO, chlorosomes, LH2, and phycobilisome were 6.4, 23.3, 9.5, and 33.4?nm, respectively. These size measurements were compared with values measured by dynamic light scattering and those reported in the literature. These complexes were deposited onto a transparent substrate by electrospray deposition. Absorption and fluorescence spectra of the deposited LHCs were measured. It was observed that the LHCs have light absorption and fluorescence spectra similar to that in solution, demonstrating the viability of the process. 相似文献
65.
Reaction between ethyl 3-N,N-(dimethylamino)-2-isocyanoacrylate (1) and a primary amine (2) regioselectively affords 1-alkyl-4-imidazolecarboxylates (3) in good yields (52-89%). The method is applicable to unhindered and hindered amine substrates, as well as those containing reactive functionality such as alcohols and secondary and tertiary amines. [reaction: see text] 相似文献
66.
Nigel T. Lucas Marie P. Cifuentes Lam T. Nguyen Mark G. Humphrey 《Journal of Cluster Science》2001,12(1):201-221
The new phosphines Ph2PC6H4-4-CCR [R=SiMe3 (1), H (2)] have been used to prepare Ru3(CO)9(Ph2PC6H4-4-CCSiMe3)3 (4) and Ru(CCC6H4-4-PPh2)(PPh3)2(-C5H5) (3), respectively, the latter with a pendent phosphine. Reaction of 4 with carbonate or fluoride affords Ru3(CO)9(Ph2PC6H4-4-CCH)3 (5) with pendent terminal alkynyl groups, the identity of which was confirmed by a structural study. Reaction of 5 with [Ru(NCMe)(PPh3)2(-C5H5)]PF6 or reaction of Ru3(CO)12 with 3 gives Ru3(CO)9{(Ph2PC6H4-4-CC)Ru(PPh3)2(-C5H5)}3 (6). Complexes 3–6 have been studied by cyclic voltammetry. Proceeding from Ru3(CO)12 to 4 or 5 shifts the cluster-centred reduction to more negative potential and affords facile cluster-centred oxidation. Proceeding from 4/5 and 3 to 6 results in similarly-located cluster-centred reduction and peripheral ruthenium-centred oxidation, but results in a lack of observable cluster-centred oxidation. Crystal data for 5·C6H14: space group P¯1, a=12.760(1) Å, b=17.077(1) Å, c=17.924(2) Å, =108.656(5)°, =96.344(5)°, =93.523(5)°, V=3658.4(6) Å3, Z=2, R=0.078, Rw=0.105 for 5008 reflections [I>2.00(I)]. 相似文献
67.
Chiosis G Timaul MN Lucas B Munster PN Zheng FF Sepp-Lorenzino L Rosen N 《Chemistry & biology》2001,8(3):289-299
BACKGROUND: The Hsp90s contain a conserved pocket that binds ATP/ADP and plays an important role in the regulation of chaperone function. Occupancy of this pocket by several natural products (geldanamycin (GM) and radicicol) alters Hsp90 function and results in the degradation of a subset of proteins (i.e. steroid receptors, Her2, Raf). We have used the structural features of this pocket to design a small molecule inhibitor of Hsp90. RESULTS: The designed small molecule PU3 competes with GM for Hsp90 binding with a relative affinity of 15-20 microM. PU3 induces degradation of proteins, including Her2, in a manner similar to GM. Furthermore, PU3 inhibits the growth of breast cancer cells causing retinoblastoma protein hypophosphorylation, G1 arrest and differentiation. CONCLUSIONS: PU3 is representative of a novel class of synthetic compounds that binds to Hsp90 and inhibits the proliferation of cancer cells. These reagents could provide a new strategy for the treatment of cancers. 相似文献
68.
de Oliveira Cristina Soltovski Bet Camila Delinski Bisinella Radla Zabian Bassetto Waiga Lucas Henrique Colman Tiago André Denck Schnitzler Egon 《Journal of Thermal Analysis and Calorimetry》2018,133(3):1491-1498
Journal of Thermal Analysis and Calorimetry - Samples of potato starch (PS), sweet potato starch (SPS) and their binary mixtures, with moisture levels of 10, 15 and 20% (db), were submitted to... 相似文献
69.
70.
De Fazio D Lucas JM Aquilanti V Cavalli S 《Physical chemistry chemical physics : PCCP》2011,13(18):8571-8582
Exact quantum reactive scattering calculations in the collision energy range 1-250 meV have been carried out for both the isotopic product channels of the title system. The dynamical studies compares an ab initio potential energy surface (PES) recently appeared in the literature (J. Chem. Phys., 2008, 129, 011103) with other phenomenological PESs. Vibrational branching ratios, cross sections and rate constants are presented and compared with molecular beam scattering experiments as well as with chemical kinetics data. In particular, the agreement of the vibrational branching ratios with experimental measurements is improved with respect to previous studies on other PESs, mainly because of the presence of a broad peak in the HF(v' = 3) integral cross section completely absent in the previous simulations. This feature, observed by molecular beam experiments, is the fingerprint of a new reaction mechanism operative in the dynamics described by the new PES. A conjecture for its origin, able to explain many of its characteristic aspects, is analyzed and discussed. 相似文献