全文获取类型
收费全文 | 4509篇 |
免费 | 144篇 |
国内免费 | 41篇 |
专业分类
化学 | 2891篇 |
晶体学 | 28篇 |
力学 | 108篇 |
数学 | 967篇 |
物理学 | 700篇 |
出版年
2023年 | 32篇 |
2022年 | 98篇 |
2021年 | 114篇 |
2020年 | 99篇 |
2019年 | 112篇 |
2018年 | 96篇 |
2017年 | 70篇 |
2016年 | 150篇 |
2015年 | 115篇 |
2014年 | 136篇 |
2013年 | 248篇 |
2012年 | 264篇 |
2011年 | 303篇 |
2010年 | 196篇 |
2009年 | 170篇 |
2008年 | 285篇 |
2007年 | 216篇 |
2006年 | 229篇 |
2005年 | 232篇 |
2004年 | 214篇 |
2003年 | 145篇 |
2002年 | 150篇 |
2001年 | 49篇 |
2000年 | 48篇 |
1999年 | 63篇 |
1998年 | 50篇 |
1997年 | 35篇 |
1996年 | 72篇 |
1995年 | 38篇 |
1994年 | 34篇 |
1993年 | 31篇 |
1992年 | 31篇 |
1991年 | 32篇 |
1990年 | 14篇 |
1989年 | 17篇 |
1988年 | 17篇 |
1987年 | 22篇 |
1986年 | 20篇 |
1985年 | 21篇 |
1984年 | 28篇 |
1982年 | 33篇 |
1981年 | 29篇 |
1980年 | 12篇 |
1979年 | 21篇 |
1978年 | 31篇 |
1977年 | 18篇 |
1976年 | 24篇 |
1974年 | 15篇 |
1973年 | 14篇 |
1972年 | 10篇 |
排序方式: 共有4694条查询结果,搜索用时 15 毫秒
921.
We formulate general conjectures about the relationship between the A-model connection on the cohomology of ad-dimensional Calabi-Yau complete intersectionV ofr hypersurfacesV
1
,...,V
r
in a toric varietyP
and the system of differential operators annihilating the special generalized hypergeometric series 0 constructed from the fan . Using this generalized hypergeometric series, we propose conjectural mirrorsV ofV and the canonicalq-coordinates on the moduli spaces of Calabi-Yau manifolds.In the second part of the paper we consider some examples of Calabi-Yau 3-folds having Picard number >1 in products of projective spaces. For conjectural mirrors, using the recurrent relation among coefficients of the restriction of the hypergeometric function 0 on a special line in the moduli space, we determine the Picard-Fuchs equation satisfied by periods of this special one-parameter subfamily. This allows to obtain some sequences of integers which can be conjecturally interpreted in terms of Gromov-Witten invariants. Using standard techniques from enumerative geometry, first terms of these sequence of integers are checked to coincide with numbers of rational curves on Calabi-Yau 3-folds. 相似文献
922.
923.
Steven S. Wesolowski Edward F. Valeev Rollin A. King Victor Baranovski Henry F. Schaefer III 《Molecular physics》2013,111(16):1227-1231
Atomic natural orbital (ANO) basis sets for calcium may produce surprisingly poor atomic and molecular properties and energetics. The weaknesses in these basis sets may be traced primarily to deficiencies within the sets of d functions which are incapable of effectively correlating the 3s and 3p electrons. Examples are given which show that addition of tight d functions to the ANO basis is required to achieve qualitatively correct energetics and structures for conventionally bonded calcium compounds. 相似文献
924.
Wendy R. Altman John Moreland Victor M. Bright 《Journal of magnetism and magnetic materials》2010,322(21):3236-3239
Magneto-optic Kerr effect (MOKE) and magnetoresistance (MR) measurements were used to measure the switching characteristics of spin-valve (SV) arrays currently being developed to trap and release superparamagnetic beads within a fluid medium. The effect of SV size on switching observed by MOKE showed that a 1 μm×8 μm SV element was found to have optimal switching characteristics. MR measurements on a single 1 μm×8 μm SV switched with either an external applied magnetic field or a local magnetic field generated by an integrated write wire (current density ranging from 106 to 107 A/cm2) confirmed the MOKE findings. The 1 μm×8 μm SV low field switching was observed to be +8 and −2 mT with two stable states at zero field; the high field switching was observed to be −18 mT. The low switching fields and the large magnetic moment of the SV trap along with our observation of minimal magnetostatic effects for dense arrays are necessary design characteristics for high-force, “switchable-magnet,” microfluidic bead trap applications. 相似文献
925.
Patents are an essential information source used to monitor, track, and analyze nanotechnology. When it comes to search nanotechnology-related patents, a keyword search is often incomplete and struggles to cover such an interdisciplinary discipline. Patent classification schemes can reveal far better results since they are assigned by experts who classify the patent documents according to their technology. In this paper, we present the most important classifications to search nanotechnology patents and analyze how nanotechnology is covered in the main patent classification systems used in search systems nowadays: the International Patent Classification (IPC), the United States Patent Classification (USPC), and the Cooperative Patent Classification (CPC). We conclude that nanotechnology has a significantly better patent coverage in the CPC since considerable more nanotechnology documents were retrieved than by using other classifications, and thus, recommend its use for all professionals involved in nanotechnology patent searches. 相似文献
926.
Arwen R. Pearson Reinhard Pahl Elena G. Kovaleva Victor L. Davidson Carrie M. Wilmot 《Journal of synchrotron radiation》2007,14(1):92-98
X‐ray exposure during crystallographic data collection can result in unintended redox changes in proteins containing functionally important redox centers. In order to directly monitor X‐ray‐derived redox changes in trapped oxidative half‐reaction intermediates of Paracoccus denitrificans methylamine dehydrogenase, a commercially available single‐crystal UV/Vis microspectrophotometer was installed on‐line at the BioCARS beamline 14‐BM‐C at the Advanced Photon Source, Argonne, USA. Monitoring the redox state of the intermediates during X‐ray exposure permitted the creation of a general multi‐crystal data collection strategy to generate true structures of each redox intermediate. 相似文献
927.
This study reports the use of quartz crystal nanobalance (QCN) to study the adsorption of two model molecules namely albumin and doxycycline by hydroxyapatite (HA). The work focuses on the deposition of a stable coating of HA on the quartz crystal, modification of the coating using doxycycline and its subsequent effects on albumin adsorption. The uniformity and thickness of the HA coating has been studied using atomic force microscopy (AFM). The functional groups to ascertain the presence of the selected moieties have been characterized by Raman spectroscopy. The results indicate that the mass of albumin deposited on the surface of the HA coated quartz crystal functionalized with doxycycline shows a substantial increase when compared to the standard HA coated quartz crystal. The adsorbed albumin has also been found to be retained for an enhanced period of time. This surface immobilization of doxycycline and subsequent albumin adsorption seem to be a promising approach to confer biomaterials with antithrombogenic and antibacterial surfaces. 相似文献
928.
Victor Callegari Philipp M. Nellen Roland Hauert Francisco Hernández-Ramírez 《Applied Surface Science》2007,253(22):8969-8973
Focused ion beam physical sputtering and iodine-enhanced etching of indium phosphide (InP) were performed. Up to 15× enhanced etching rates over sputtering were measured at room temperature, due to the addition of iodine to the sputter-process. Reaction mechanisms and products are discussed and characterized. The reaction is limited by the desorption of indium triiodide (InI3) at room temperature. InI3 has to be removed by sputtering, which simultaneously amorphizes the underlying substrate. Surface roughness and stoichiometry of InP are compared for sputtering and etching. Gallium-contamination and the damaged zone in InP are significantly reduced by iodine-enhanced etching. Based on the reaction mechanisms, an optimum beam scanning strategy is proposed which allows precise microfabrication in reduced time and minimizes damage to the substrate. The method is also applicable for other halide gas etching processes of III-V semiconductors. 相似文献
929.
Katalin E. Kövér Dušan Uhr?&#x;n Victor J. Hruby 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):162-168
A pulsed field gradient version of the sensitivity-enhanced 2D TOCSY experiment is proposed which yields high-quality spectra with improved sensitivity and a minimum of two scans pert1increment. For rapid acquisition of 1D TOCSY spectra, the 1D DPFGSE–TOCSY experiment was modified to include phase-encoded multiple-selective excitation followed by a simple spectral editing. Combination of these two building blocks is used in a sensitivity-enhanced 2D analog of the 3D TOCSY–TOCSY experiment which provides an efficient tool for resolving severely overlapped signals of oligomers in short experimental time. 相似文献
930.
We discover that a spatially localized gain supports stable vortex solitons in media with cubic nonlinearity and two-photon absorption. The interplay between nonlinear losses and gain in amplifying rings results in the suppression of otherwise ubiquitous azimuthal modulation instabilities of radially symmetric vortex solitons. We find that the topology of the gain profile imposes restrictions on the maximal possible charge of vortex solitons. Symmetry breaking occurs at high gain levels, resulting in the formation of necklace vortex solitons composed of asymmetric bright spots. 相似文献