全文获取类型
| 收费全文 | 7202篇 |
| 免费 | 148篇 |
| 国内免费 | 55篇 |
专业分类
| 化学 | 4309篇 |
| 晶体学 | 67篇 |
| 力学 | 114篇 |
| 数学 | 1315篇 |
| 物理学 | 1600篇 |
出版年
| 2024年 | 20篇 |
| 2023年 | 36篇 |
| 2022年 | 148篇 |
| 2021年 | 199篇 |
| 2020年 | 171篇 |
| 2019年 | 248篇 |
| 2018年 | 206篇 |
| 2017年 | 176篇 |
| 2016年 | 269篇 |
| 2015年 | 230篇 |
| 2014年 | 229篇 |
| 2013年 | 494篇 |
| 2012年 | 441篇 |
| 2011年 | 552篇 |
| 2010年 | 379篇 |
| 2009年 | 315篇 |
| 2008年 | 444篇 |
| 2007年 | 407篇 |
| 2006年 | 372篇 |
| 2005年 | 358篇 |
| 2004年 | 310篇 |
| 2003年 | 249篇 |
| 2002年 | 199篇 |
| 2001年 | 90篇 |
| 2000年 | 87篇 |
| 1999年 | 102篇 |
| 1998年 | 78篇 |
| 1997年 | 55篇 |
| 1996年 | 89篇 |
| 1995年 | 50篇 |
| 1994年 | 46篇 |
| 1993年 | 53篇 |
| 1992年 | 41篇 |
| 1991年 | 31篇 |
| 1990年 | 15篇 |
| 1989年 | 17篇 |
| 1988年 | 10篇 |
| 1987年 | 10篇 |
| 1986年 | 12篇 |
| 1985年 | 15篇 |
| 1984年 | 14篇 |
| 1983年 | 18篇 |
| 1982年 | 14篇 |
| 1981年 | 13篇 |
| 1979年 | 8篇 |
| 1978年 | 11篇 |
| 1977年 | 12篇 |
| 1976年 | 6篇 |
| 1975年 | 11篇 |
| 1973年 | 5篇 |
排序方式： 共有7405条查询结果，搜索用时 15 毫秒
961.
Svetlana G. Churusova Diana V. Aleksanyan Andrei A. Vasil'ev Ekaterina Yu. Rybalkina Olga Yu. Susova Zinaida S. Klemenkova Rinat R. Aysin Yulia V. Nelyubina Vladimir A. Kozlov 《应用有机金属化学》2018,32(6)
Pincer complexes featuring readily tunable tridentate ligand frameworks comprise one of the most actively studied classes of organometallic and metal–organic compounds and find extensive use in catalysis, organic synthesis, materials science, and other fields of chemistry and allied disciplines. Currently growing attention is devoted to non‐classical ligand scaffolds, such as functionalized carboxamides, which offer multiple options for directed structural modifications. In this study, the reactions of (methylsulfanyl)acetyl and propanoyl chlorides with 2‐(aminomethyl)pyridine, 2‐(2‐aminoethyl)pyridine, 8‐aminoquinoline and 2‐(diphenylthiophosphoryl)aniline afford a series of new pincer‐type ligands based on functionalized carboxamides. The ligands obtained readily undergo direct cyclopalladation under the action of PdCl2(NCPh)2 in dichloromethane at room temperature, resulting in Pd(II) pincer complexes with N,N,S‐ and S,N,S‐donor sets. Importantly, some of the cyclopalladated derivatives can also be produced efficiently under solvent‐free conditions according to the approach recently developed by our group. The complexes obtained have been tested for cytotoxicity against several human cancer cell lines and catalytic activity in the model Suzuki reaction. The results have been compared to those for the related Pd(II) pincer complexes to define the main structure–activity relationships and to outline the most promising structures for further investigations. 相似文献
962.
Dr. Vladimir Pelmenschikov Dr. Leland B. Gee Dr. Hongxin Wang Dr. K. Cory MacLeod Sean F. McWilliams Dr. Kazimer L. Skubi Prof. Dr. Stephen P. Cramer Prof. Dr. Patrick L. Holland 《Angewandte Chemie (International ed. in English)》2018,57(30):9367-9371
High‐spin iron species with bridging hydrides have been detected in species trapped during nitrogenase catalysis, but there are few general methods of evaluating Fe?H bonds in high‐spin multinuclear iron systems. An 57Fe nuclear resonance vibrational spectroscopy (NRVS) study on an Fe(μ‐H)2Fe model complex reveals Fe?H stretching vibrations for bridging hydrides at frequencies greater than 1200 cm?1. These isotope‐sensitive vibrational bands are not evident in infrared (IR) spectra, showing the power of NRVS for identifying hydrides in this high‐spin iron system. Complementary density functional theory (DFT) calculations elucidate the normal modes of the rhomboidal iron hydride core. 相似文献
963.
Dr. Cindy C. Pham Dr. David W. Mulder Dr. Vladimir Pelmenschikov Dr. Paul W. King Dr. Michael W. Ratzloff Dr. Hongxin Wang Nakul Mishra Dr. Esen E. Alp Dr. Jiyong Zhao Dr. Michael Y. Hu Dr. Kenji Tamasaku Dr. Yoshitaka Yoda Prof. Stephen P. Cramer 《Angewandte Chemie (International ed. in English)》2018,57(33):10605-10609
A combination of nuclear resonance vibrational spectroscopy (NRVS), FTIR spectroscopy, and DFT calculations was used to observe and characterize Fe?H/D bending modes in CrHydA1 [FeFe]‐hydrogenase Cys‐to‐Ser variant C169S. Mutagenesis of cysteine to serine at position 169 changes the functional group adjacent to the H‐cluster from a ‐SH to ‐OH, thus altering the proton transfer pathway. The catalytic activity of C169S is significantly reduced compared to that of native CrHydA1, presumably owing to less efficient proton transfer to the H‐cluster. This mutation enabled effective capture of a hydride/deuteride intermediate and facilitated direct detection of the Fe?H/D normal modes. We observed a significant shift to higher frequency in an Fe?H bending mode of the C169S variant, as compared to previous findings with reconstituted native and oxadithiolate (ODT)‐substituted CrHydA1. On the basis of DFT calculations, we propose that this shift is caused by the stronger interaction of the ‐OH group of C169S with the bridgehead ‐NH‐ moiety of the active site, as compared to that of the ‐SH group of C169 in the native enzyme. 相似文献
964.
Vladimir A. D&#x;yakonov Gulnara N. Kadikova Lilya U. Dzhemileva Guzel F. Gazizullina Milyausha M. Yunusbaeva Usein M. Dzhemilev 《Tetrahedron》2018,74(30):4071-4077
Bicyclo[4.3.1]deca-2,4,8-triene-7,10-diols were synthesized in 76–85% yields by oxidative skeletal isomerization of the substituted bicyclo[4.2.2]deca-2,4,7,9-tetraenes of various structures on treatment with m-chloroperbenzoic acid. The structures of the obtained bicyclic unsaturated diols were reliably proven by modern spectral methods and X-ray diffraction. A high antitumor activity in vitro was found for bicyclo[4.3.1]deca-2,4,8-triene-7,10-diols against the Jurkat, K562, U937 and HL-60 tumor cell lines. 相似文献
965.
966.
Hani Kbashi Sergey V. Sergeyev Chengbo Mou Amos Martinez Garcia Mohammed Al Araimi Aleksei Rozhin Stanislav Kolpakov Vladimir Kalashnikov 《Annalen der Physik》2018,530(5)
During the last two decades, revealing mechanisms of origin waves with anomalous amplitude (rogue waves) have been in the focus of researchers from different fields ranging from oceanography to laser physics. Mode‐locked lasers, as a test bed system, provide a unique opportunity to collect more data on rogue waves in the form of random pulses (soliton rain) and to clarify the mechanisms of rogue‐wave emergence caused by soliton–soliton and soliton–dispersive wave interactions. Here, for the first time, for an Er‐doped mode‐locked laser, a new type of vector rogue waves is demonstrated experimentally and theoretically, which is driven by desynchronization of the orthogonal linear states of polarization, so leading to output power oscillations in the form of anomalous spikes‐dips (bright‐dark rogue waves). The results can pave the way to unlocking the universal nature of the origin of rogue waves and thus can be of interest to the broad scientific community. 相似文献
967.
The emphasis of this review is both the geometric realization of the 2-point velocity correlation tensor field Bij (x,x′,t) and isometries of the correlation space K3 equipped with a (pseudo-) Riemannian metrics ds2(t) generated by the tensor field. The special form of this tensor field for homogeneous isotropic turbulence specifies ds2(t) as the semi-reducible pseudo-Riemannian metric. This construction presents the template for the application of methods of Riemannian geometry in turbulence to observe, in particular, the deformation of length scales of turbulent motion localized within a singled out fluid volume of the flow in time. This also allows to use common concepts and technics of Lagrangian mechanics for a Lagrangian system (Mt, ds2(t)), Mt ? K3. Here the metric ds2(t), whose components are the correlation functions, evolves due to the von Kármán-Howarth equation. We review the explicit geometric realization of ds2(t) in K3 and present symmetries (or isometric motions in K3) of the metric ds2(t) which coincide with the sliding deformation of a surface arising under the geometric realization of ds2(t). We expose the fine structure of a Lie algebra associated with this symmetry transformation and construct the basis of differential invariants. Minimal generating set of differential invariants is derived. We demonstrate that the well-known Taylor microscale λg is a second-order differential invariant and show how λg can be obtained by the minimal generating set of differential invariants and the operators of invariant differentiation. Finally, we establish that there exists a nontrivial central extension of the infinite-dimensional Lie algebra constructed wherein the central charge is defined by the same bilinear skew-symmetric form c as for the Witt algebra which measures the number of internal degrees of freedom of the system. For turbulence, we give the asymptotic expansion of the transversal correlation function for the geometry generated by a quadratic form. 相似文献
968.
Valeri Lapanik Sergei Timofeev Genadz Sasnouski Vladimir Bezborodov Wolfgang Haase 《Liquid crystals》2017,44(2):297-302
We report on chiral-nematic mixtures containing viscous chiral dopants, composed of rigid rod-like chiral molecules, in order to solve the problem of backflow in the middle layers of the liquid crystal cells. During the study, the viscoelastic properties of the liquid crystal compositions have been optimised, as well as the helical twisting power of the chiral compounds, the anchoring energy and the pre-tilt angle of alignment materials, the ratio between the cell gap and the helical pitch (d/P0). After optimisation, we prepared test cells with low operating voltage – from 1.5 till 5.0 V, fast response time (τon + τoff) – less than 1 ms, wide operating temperature range from ?40°C till +100°C, and good thermal stability. It should be noted that the response time of the new electro-optical mode does not strongly depend on the cell gap, which is in contrast to other known operating modes. We have achieved rather linear than quadratic dependence of the response time when changing the thickness of the cell. 相似文献
969.
Tatiana B. Mikenas Evgeny I. Koshevoy Vladimir A. Zakharov 《Journal of polymer science. Part A, Polymer chemistry》2017,55(14):2298-2308
The structure and formation of polyethylene (PE) particles on supported titanium–magnesium catalysts having different structural characteristics (sizes of microcrystallites, mesopores, and subparticles) were studied for the first time. Scanning electron microscopy was used to identify structural elements of the polymer particles formed over such catalysts and to reveal morphological changes in the growing polymer particles when the yield was increased from approximately 0.2 g PE/g catalyst to approximately 13 kg PE/g catalyst. A relationship was found between structural characteristics of the porous catalyst particles, morphology of the nascent polymer particles, and bulk density of the polymer powder. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2298–2308 相似文献
970.