全文获取类型
收费全文 | 327篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 238篇 |
晶体学 | 5篇 |
力学 | 8篇 |
数学 | 31篇 |
物理学 | 50篇 |
出版年
2019年 | 3篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 14篇 |
2012年 | 9篇 |
2011年 | 11篇 |
2010年 | 6篇 |
2009年 | 8篇 |
2008年 | 9篇 |
2007年 | 13篇 |
2006年 | 3篇 |
2005年 | 10篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 11篇 |
2001年 | 3篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 13篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 8篇 |
1969年 | 2篇 |
1965年 | 2篇 |
1963年 | 2篇 |
1962年 | 8篇 |
1960年 | 3篇 |
1958年 | 7篇 |
1957年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有332条查询结果,搜索用时 281 毫秒
1.
Etiënne L. M. Vermeirssen Conrad Dietschweiler Beate I. Escher Jürgen van der Voet Juliane Hollender 《Analytical and bioanalytical chemistry》2013,405(15):5225-5236
The Chemcatcher passive sampler, which uses Empore? disks as sampling phase, is frequently used to monitor polar organic chemicals in river water and effluents. Uptake kinetics need to be quantified to calculate time-weighted average concentrations from Chemcatcher field deployments. Information on release kinetics is needed if performance reference compounds (PRCs) are used to quantify the influence of environmental conditions on the uptake. In a series of uptake and elimination experiments, we used Empore? SDB disks (poly(styrenedivinylbenzene) copolymer modified with sulfonic acid groups) as a sampling phase and 22 compounds with a logK ow (octanol–water partitioning coefficient) range from ?2.6 to 3.8. Uptake experiments were conducted in river water or tap water and lasted up to 25 days. Only 1 of 22 compounds (sulfamethoxazole) approached equilibrium in the uptake trials. Other compounds showed continuing non-linear uptake, even after 25 days. All compounds could be released from SDB disks, and desorption was proportionally higher in disks loaded for shorter periods. Desorption showed two-phase characteristics, and desorption was proportionally higher for passively sorbed compounds compared to actively loaded compounds (active loading was performed by pulling spiked river water over SDB disks using vacuum). We hypothesise that the two-phase kinetics and better retention of actively loaded compounds—and compounds loaded for a longer period—may be caused by slow diffusion of chemicals within the polymer. As sorption and desorption did not show isotropic kinetics, it is not possible to develop robust PRCs for adsorbent material like SDB disks. 相似文献
2.
Marcello Bernardara Emanuele Macrì Sukhendu Mehrotra Paolo Stellari 《Advances in Mathematics》2012,229(2):770-803
We prove a categorical version of the Torelli theorem for cubic threefolds. More precisely, we show that the non-trivial part of a semi-orthogonal decomposition of the derived category of a cubic threefold characterizes its isomorphism class. 相似文献
3.
Epi Erpina Latifah Kosim Darusman Arum Vitasari Budi Riza Putra Eti Rohaeti 《液相色谱法及相关技术杂志》2017,40(12):635-639
A new method for simultaneous quantification of curcuminoids and xanthorrhizol (XNT) in Curcuma xanthorrhiza was developed and validated using high-performance liquid chromatography with diode-array UV–Vis detector. The chromatographic separation was achieved on a Phenomenex C18 at room temperature with the mobile-phase acetonitrile ?0.001% formic acid in gradient elution system and delivered at a flow rate of 1?mL/min. Detection wavelength 425?nm was used for curcuminoids and 224?nm for XNT. System suitability, linearity, precision, accuracy, limit of detection, limit of quantitation, and stability were evaluated and were found in good agreement with Association of Official Analytical Chemists guidelines for single-laboratory validation. The proposed method was found to be precise, accurate, and reliable and also could be applied for the simultaneous quantitative analysis of curcuminoids and XNT in C. xanthorriza raw material and its herbal medicinal product. 相似文献
4.
We present branching-on-hyperplane methods for solving mixed integer linear and mixed integer convex programs. In particular,
we formulate the problem of finding a good branching hyperplane using a novel concept of adjoint lattice. We also reformulate
the problem of rounding a continuous solution to a mixed integer solution. A worst case complexity of a Lenstra-type algorithm
is established using an approximate log-barrier center to obtain an ellipsoidal rounding of the feasible set. The results
for the mixed integer convex programming also establish a complexity result for the mixed integer second order cone programming
and mixed integer semidefinite programming feasibility problems as a special case. Our results motivate an alternative reformulation
technique and a branching heuristic using a generalized (e.g., ellipsoidal) norm reduced basis available at the root node. 相似文献
5.
We generalize the disjunctive approach of Balas, Ceria, and Cornuéjols [2] and devevlop a branch-and-cut method for solving
0-1 convex programming problems. We show that cuts can be generated by solving a single convex program. We show how to construct
regions similar to those of Sherali and Adams [20] and Lovász and Schrijver [12] for the convex case. Finally, we give some
preliminary computational results for our method.
Received January 16, 1996 / Revised version received April 23, 1999?Published online June 28, 1999 相似文献
6.
Eti Mehrotra Jyotsna Vishwakarma Avinash C. Tripathi Pankaj K. Sonar 《Natural product research》2019,33(4):568-572
The present study explored the schizonticidal potential of traditionally used Magnolia champaca (L.) Baill. ex. Pierre flowers, identifying constituents of interest. The extraction of phytoconstituents was carried out by microwave-assisted technique, isolated via column chromatography, and characterised by various physicochemical, spectral (IR, 1H-NMR and Mass) and chromatographic (HPTLC) techniques. Both the isolated compounds (parthenolide and costunolide diepoxide) exhibited potent schizonticidal antimalarial activity during primary screening in rodent models, with maximum parasitaemia suppression (85.18% and 83.65%, respectively) at a dose of 20 mg/kg body weight when compared to the standard drugs chloroquine and artesunate. In silico techniques were employed to identify the probable biological target and mechanism of action of these isolated compounds. Molecular docking studies also predicted the binding orientations and multi-targeted action of these compounds, in particular costunolide diepoxide with maximum affinity towards SERCA and DHFR proteins. Additionally, favourable in silico ADMET parameters were envisaged through various computational programmes. 相似文献
7.
The phenomenon of proton emission is treated as a process of asymmetric fission through a one-dimensional potential barrier
developed due to combined effects of the Coulomb potential, centrifugal potential and various renormalization processes. The
barrier is simulated to an asymmetric, smooth and analytically solvable potential with adjustable depth, shape and range.
The half-lives of proton emitters in the mass range A = 105–171 have been calculated using exact expression for the transmission coefficients. Good agreement with the experimental
data is obtained by the adjustment of just one parameter in all the cases.
相似文献
8.
Nitin Mehrotra Sreedharan Sabarinath Satyendra Suryawanshi Kanwal Raj Ram Chandra Gupta 《Chromatographia》2009,69(9-10):1077-1082
The herbal medicament derived from the lipid soluble fraction obtained from Curcuma longa L. (Zingiberaceae) has shown potential neuroprotective activity in disorders like stroke. HM has been standardized with three biomarkers: ar-turmerone, α/β-turmerone and curlone, major bisabolane sesquiterpenes of turmeric oil. Development of a biaonalytical method for these sesquiterpenes was initiated to characterize its preclinical pharmacokinetics in rabbits to accelerate its development as a potential candidate for vascular complications. Since, the compounds are structurally and chemically very similar, gradient elution was utilized on a C-18 reversed phase column with a mobile phase comprising of acetonitrile and deionised water. The UV detector was set at wavelengths 240 and 270 nm. The sample clean-up was performed by protein precipitation with acetonitrile. The method was reasonably sensitive with limits of quantitation (LOQ) of 0.098 μg mL?1 in plasma for all the analytes. Accuracy and precision were within the acceptable limits, as indicated by relative standard deviation (% RSD) varying from 1.3 to 13.6% and bias values ranging from ?5.5 to 10.3%, respectively. Moreover, the analytes were stable in plasma even after three freeze-thaw cycles. The method was applied to generate preliminary pharmacokinetics of turmeric oil in rabbits after intravenous administration. 相似文献
9.
We prove that arbitrary (nonpolynomial) scalar evolution equations of order m ≥ 7 , that are integrable in the sense of admitting the canonical conserved densities ρ(1) , ρ(2) , and ρ(3) introduced in [ 1 ], are polynomial in the derivatives u m − i for i = 0, 1, 2. We also introduce a grading in the algebra of polynomials in u k with k ≥ m − 2 over the ring of functions in x , t , u , … , u m −3 and show that integrable equations are scale homogeneous with respect to this grading . 相似文献
10.
We study the problem of suitably locating US Coast Guard air stations to respond to emergency distress calls. Our goal is to identify robust locations in the presence of uncertainty in distress call locations. Our analysis differs from the literature primarily in the way we model this uncertainty. In our optimization and simulation based methodology, we develop a statistical model and demonstrate our procedure using a real data set of distress calls. In addition to guiding strategic decisions of placement of various stations, our methodology is also able to provide guidance on how the resources should be allocated across stations. 相似文献