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621.
623.
As part of the national survey to evaluate natural radioactivity in the environment, concentration levels of total radioactivity and natural uranium have been analysed in drinking water samples. A survey to study natural radioactivity in drinking waters was carried out in the Van province, East Turkey. Twenty-three samples of drinking water were collected in the Van province and analysed for total α, total β and 238U activity. The total α and total β activities were counted by using the α/β counter of the multi-detector low background system (PIC MPC-9604), and the 238U concentrations were determined by inductively coupled plasma-mass spectrometry (Thermo Scientific Element 2). The samples were categorised according to origin: tap, spring or mineral supply. The activity concentrations for total α were found to range from 0.002 to 0.030 Bq L?1 and for total β from 0.023 to 1.351 Bq L?1. Uranium concentrations ranging from 0.562 to 14.710 μg L?1 were observed in drinking waters. Following the World Health Organisation rules, all investigated waters can be used as drinking water. 相似文献
624.
Mehrdad Pourayoubi Mozhgan Abrishami Vclav Eigner Marek Ne
as Michal Duek Mahmoud Delavar 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(12):1147-1152
The compound N,N′,N′′‐tricyclohexylphosphorothioic triamide, C18H36N3PS or P(S)[NHC6H11]3, (I), crystallizes in the space group Pnma with the molecule lying across a mirror plane; one N atom lies on the mirror plane, whereas the bond‐angle sum at the other N atom has a deviation of some 8° from the ideal value of 360° for a planar configuration. The orientation of the atoms attached to this nonplanar N atom corresponds to an anti orientation of the corresponding lone electron pair (LEP) with respect to the P=S group. The P=S bond length of 1.9785 (6) Å is within the expected range for compounds with a P(S)[N]3 skeleton; however, it is in the region of the longest bond lengths found for analogous structures. This may be due to the involvement of the P=S group in N—H...S=P hydrogen bonds. In O,O′‐diethyl (2‐phenylhydrazin‐1‐yl)thiophosphonate, C10H17N2O2PS or P(S)[OC2H5]2[NHNHC6H5], (II), the bond‐angle sum at the N atom attached to the phenyl ring is 345.1°, whereas, for the N atom bonded to the P atom, a practically planar environment is observed, with a bond‐angle sum of 359.1°. A Cambridge Structural Database [CSD; Allen (2002). Acta Cryst. B 58 , 380–388] analysis shows a shift of the maximum population of P=S bond lengths in compounds with a P(S)[O]2[N] skeleton to the shorter bond lengths relative to compounds with a P(S)[N]3 skeleton. The influence of this difference on the collective tendencies of N...S distances in N—H...S hydrogen bonds for structures with P(S)[N]3 and P(S)[O]2[N] segments were studied through a CSD analysis. 相似文献
625.
Gyula O. H. Katona Attila Sali Klaus-Dieter Schewe 《Central European Journal of Mathematics》2008,6(1):1-11
The following problem motivated by investigation of databases is studied. Let be a q-ary code of length n with the properties that has minimum distance at least n − k + 1, and for any set of k − 1 coordinates there exist two codewords that agree exactly there. Let f(q, k)be the maximum n for which such a code exists. f(q, k)is bounded by linear functions of k and q, and the exact values for special k and qare determined.
相似文献
626.
Lucas Almir Cavalcante Minho Zenilda de Lourdes Cardeal Helvécio Costa Menezes 《Journal of separation science》2023,46(19):2300187
Among the main approaches for predicting the spatial positions of eluates in comprehensive two-dimensional gas chromatography, the still under-explored computational models based on deep learning algorithms emerge as robust and reliable options due to their high adaptability to the structure and complexity of the data. In this work, an open-source program based on deep neural networks was developed to optimize chromatographic methods and simulate operating conditions outside the laboratory. The deep neural networks models were fit to convenient experimental predictors, resulting in scaled losses (mean squared error) equivalent to 0.006 (relative average deviation = 8.56%, R2 = 0.9202) and 0.014 (relative average deviation = 1.67%, R2 = 0.8009) in the prediction of the first- and second-dimension retention times, respectively. Good compliance was observed for the main chemical classes, such as environmental contaminants: volatile, semivolatile organic compounds, and pesticides; biochemistry molecules: amino acids and lipids; pharmaceutical industry and personal care products and residues: drugs and metabolites; among others. On the other hand, there is a need for continuous database updates to predict retention times of less common compounds accurately. Thus, forming a collaborative database is proposed, gathering voluntary findings from other users. 相似文献
627.
针对测量船传统实时水平测量方法精度较低(≥10.0″)的问题,引入了基于光学测量手段的动态实时船体水平姿态测量方法。采用"光学编码精密测角+惯性同步复示平台+水平误差检测工具"的设计模式,保证了跟踪的稳定性,提高了测量精度。实验结果表明:提出的方法可以提供比传统惯导系统更稳定、精度更高(纵摇5.37″,横摇3.60″)的船体水平姿态数据;可以作为一种普遍适用的运动载体精密水平测量监测手段,为运动载体实时提供高精度的水平基准信息,或用于运动载体惯导水平精度鉴定等。 相似文献
628.
以国家材料科学数据共享网为依托,我们建立了一个大型的高分子材料数据库并已向公众开放访问。数据库主要面向科研工作人员和工业企业等,提供基于高分子材料工业产品信息的数据共享服务。该数据库涵盖塑料、橡胶、纤维、涂料、胶粘剂、加工助剂等高分子领域主要的材料类型,目前已纳入7 000余个牌号的50 000多条数据。针对高分子材料类型的复杂性,该数据库采取了网状带冗余的分类方式以使一些组成复杂的材料可通过多种分类路径查询到。数据入库前,通过在数据生产、搜集、整合等多个过程中的评估以确保数据质量和可靠性。入库的数据也从数据来源、评估结果、修改记录等多个方面进行标记,以便后期进一步进行核对与评估。 相似文献
629.
《Analytical letters》2012,45(5):753-792
The aim of this review is to present a very concise report of the research activities in the area of Analytical Chemistry performed in Greece during the last decade. Since, research in chemical analysis conducted by Greek scientific institutions covers a very large variety of analytical methodologies and techniques, it is found preferable to organize this review based on a separate presentation of the scientific activities of each Greek University or Scientific Institution, operating analytical laboratories or other divisions involved in analytical chemistry research. 相似文献
630.
Environment issues are more than ever important in a modern society. Complying with stricter legal thresholds on pollution emissions raises an important economic issue. This paper presents some ideas in the use of optimization tools to help in the planning and control of stationary pollution sources. 相似文献