全文获取类型
收费全文 | 911篇 |
免费 | 38篇 |
国内免费 | 2篇 |
专业分类
化学 | 731篇 |
晶体学 | 3篇 |
力学 | 10篇 |
数学 | 86篇 |
物理学 | 121篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 34篇 |
2021年 | 49篇 |
2020年 | 14篇 |
2019年 | 18篇 |
2018年 | 16篇 |
2017年 | 9篇 |
2016年 | 33篇 |
2015年 | 27篇 |
2014年 | 23篇 |
2013年 | 49篇 |
2012年 | 63篇 |
2011年 | 66篇 |
2010年 | 39篇 |
2009年 | 40篇 |
2008年 | 49篇 |
2007年 | 73篇 |
2006年 | 50篇 |
2005年 | 48篇 |
2004年 | 39篇 |
2003年 | 42篇 |
2002年 | 27篇 |
2001年 | 15篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 11篇 |
1997年 | 4篇 |
1996年 | 17篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 9篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1978年 | 2篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1970年 | 1篇 |
1968年 | 2篇 |
1967年 | 1篇 |
1961年 | 1篇 |
1943年 | 2篇 |
排序方式: 共有951条查询结果,搜索用时 31 毫秒
61.
3,5-Dicyano-1,4-dihydropyridines underwent ring contraction to give functionalized cyclopentadienes upon treatment with trifluoroacetic anhydride. 相似文献
62.
Elisabetta Tornatore Stefania Maria Buccellato Pasquale Vetro 《Rendiconti del Circolo Matematico di Palermo》2006,55(2):223-240
We propose a stochastic disease model where vaccination is included and such that the immunity isn’t permanent. The existence,
uniqueness and positivity of the solution and the stability of disease free equilibrium is studied. The numerical simulation
is done. 相似文献
63.
Stefano Cianchetta Luca Bregoli Stefania Galletti 《Applied biochemistry and biotechnology》2017,183(3):876-892
Giant reed, miscanthus, and switchgrass are considered prominent lignocellulosic feedstocks to obtain fermentable sugars for biofuel production. The bioconversion into sugars requires a delignifying pre-treatment step followed by hydrolysis with cellulase and other accessory enzymes like xylanase, especially in the case of alkali pre-treatments, which retain the hemicellulose fraction. Blends richer in accessory enzymes than commercial mix can be obtained growing fungi on feedstock-based substrates, thus ten selected Trichoderma isolates, including the hypercellulolytic strain Trichoderma reesei Rut-C30, were grown on giant reed, miscanthus, or switchgrass-based substrates. The produced enzymes were used to saccharify the corresponding feedstocks, compared to a commercial enzymatic mix (6 FPU/g). Feedstocks were acid (H2SO4 0.2–2%, w/v) or alkali (NaOH 0.02–0.2%, w/v) pre-treated. A microplate-based approach was chosen for most of the experimental steps due to the large number of samples. The highest bioconversion was generally obtained with Trichoderma harzianum Or4/99 enzymes (78, 89, and 94% final sugar yields at 48 h for giant reed, miscanthus, and switchgrass, respectively), with significant increases compared to the commercial mix, especially with alkaline pre-treatments. The differences in bioconversion yields were only partially caused by xylanases (maximum R 2 = 0.5), indicating a role for other accessory enzymes. 相似文献
64.
Tosi G Conti C Giorgini E Ferraris P Garavaglia MG Sabbatini S Staibano S Rubini C 《The Analyst》2010,135(12):3213-3219
Fourier transform infrared (FTIR) microspectroscopy has been employed to investigate benign (ordinary dermal and Reed nevi), dysplastic and malignant (invasive melanoma) skin lesions through the analysis of spectral changes of melanocytes as well as in the evaluation of the presence of melanin. Hierarchical cluster analysis and principal component analysis led to a satisfactory separation of malignant from dysplastic and normal melanocytes. Also, on enlarging the clustering with spectra from Reed and dermal nevi, the multivariate analysis segregated well the spectral data into discrete clusters, allowing the obtaining of reliable average spectra for analysis at the molecular level of the main groups or components responsible for the biological and biochemical changes. The most significant spectral characteristics appear to be related to differences in secondary protein structures, in nucleic acid conformation, in intra- and intermolecular bonding. In all cases, supervised and unsupervised spectral analyses resulted in satisfactory agreement with histopathological findings. 相似文献
65.
Short malonyl dehydro peptides have been epoxidized using H2O2/Na2WO4 dihydrate. The obtained diastereomeric epoxides were separated by HPLC and successfully tested in the ring opening reaction with N-Boc l-cysteine methyl ester, to indicate their electrophilic behavior. Moreover, by a simple two-step reaction, the epoxy malonyl peptides can be converted into the corresponding aziridino malonyl peptides. 相似文献
66.
We report on full-dimensional vibrational quantum dynamics of the highly excited ammonia isotopologue NHD(2) using a newly developed potential energy surface and the MCTDH program package. The calculations allow to realistically simulate an infrared laser induced stereomutation reaction at the pyramidal nitrogen atom in the femtosecond time domain. Our results allow for a thorough qualitative and quantitative understanding of infrared photoinduced stereomutation kinetics, the underlying quantum dynamics, and the reaction mechanisms. Comparison is made with a previous, reduced dimensionality study of the same reaction [R. Marquardt, M. Quack, I. Thanopulos, and D. Luckhaus, J. Chem. Phys. 118, 643 (2003)], and it is shown that slight variances of reduced spaces lead to significantly different kinetics. Because the quantum dynamics depends subtly on variances of reduced spaces, reduced dimensionality treatments are not reliable even for qualitative predictions of the stereomutation kinetics. The first direct comparison between the Multiconfigurational Time Dependent Hartree [M. H. Beck, A. Ja?ckle, G. A. Worth et al., Phys. Rep. 324, 1 (2000)] and Unimolecular Reactions Induced by Monochromatic Infrared Radiation [M. Quack and E. Sutcliffe, QCPE Bulletin 6, 98 (1986)] program packages on a specific, four dimensional quantum dynamical problem allows for their full validation in the present work. 相似文献
67.
R. Baur A. Breskin R. Chechik A. Drees C. Jacob U. Faschingbauer P. Fischer Z. Fraenkel E. Gatti P. Gl?ssel Th. G��nzel C. P. de los Heros F. Hess D. Irmscher B. Lenkeit L. H. Olsen Y. Panebrattsev A. Pfeiffer I. Ravinovich P. Rehak A. Sch?n J. Schukraft M. Sampietro A. Shor H. J. Specht V. Steiner S. Tapprogge G. Tel-Zur I. Tserruya Th. Ullrich J. P. Wurm 《The European Physical Journal C - Particles and Fields》2011,71(1):571-577
The CERES experiment has measured inclusive photon production in S-Au collisions of 200 GeV/nucleon at the CERN SPS. No evidence for direct emission of photons was found. For the kinematic region 2.1<y<2.65 and 0.4 GeV/c<p??<2.0 GeV/c the yield andp??-dependence of the observed photons are well reproduced by hadron decays. Furthermore, their production rate is found to be proportional to the charged particle density. The systematic errors comparing the measured and expected photon yield result in an upper limit of 14% for the emission of direct photons in central S-Au collisions. For a photon source with a yield depending quadratically on the charged particle density the limit can be reduced to 7%. 相似文献
68.
Gatti D Coluccelli N Gambetta A Di Lieto A Tonelli M Galzerano G Laporta P Marangoni M 《Optics letters》2011,36(19):3921-3923
The low-frequency tail of an octave-spanning supercontinuum (SC) generated by an Er:fiber comb is enhanced by a multipass Ho:YLF amplifier and used in a sum-frequency-generation scheme to obtain absolute referencing of a single-mode Tm-Ho:YAG laser tunable around 2.09 μm. By tuning the comb repetition frequency, the probing laser is scanned across the absorption lines of a CO(2) gas sample and highly accurate absorption profiles are measured. This approach can be readily scaled to any wavelength above ~2 μm. 相似文献
69.
Frank Lenzen Florian Becker Jan Lellmann Stefania Petra Christoph Schnörr 《Computational Optimization and Applications》2013,54(2):371-398
We introduce a class of adaptive non-smooth convex variational problems for image denoising in terms of a common data fitting term and a support functional as regularizer. Adaptivity is modeled by a set-valued mapping with closed, compact and convex values, that defines and steers the regularizer depending on the variational solution. This extension gives rise to a class of quasi-variational inequalities. We provide sufficient conditions for the existence of fixed points as solutions, and an algorithm based on solving a sequence of variational problems. Denoising experiments with spatial and spatio-temporal image data and an adaptive total variation regularizer illustrate our approach. 相似文献
70.