全文获取类型
收费全文 | 2810篇 |
免费 | 43篇 |
国内免费 | 11篇 |
专业分类
化学 | 1901篇 |
晶体学 | 11篇 |
力学 | 42篇 |
数学 | 617篇 |
物理学 | 293篇 |
出版年
2018年 | 18篇 |
2016年 | 35篇 |
2015年 | 36篇 |
2014年 | 35篇 |
2013年 | 104篇 |
2012年 | 60篇 |
2011年 | 79篇 |
2010年 | 44篇 |
2009年 | 72篇 |
2008年 | 86篇 |
2007年 | 67篇 |
2006年 | 74篇 |
2005年 | 84篇 |
2004年 | 84篇 |
2003年 | 70篇 |
2002年 | 70篇 |
2001年 | 64篇 |
2000年 | 51篇 |
1999年 | 26篇 |
1998年 | 41篇 |
1997年 | 51篇 |
1996年 | 48篇 |
1995年 | 34篇 |
1994年 | 51篇 |
1993年 | 47篇 |
1992年 | 48篇 |
1991年 | 36篇 |
1990年 | 45篇 |
1989年 | 61篇 |
1988年 | 68篇 |
1987年 | 67篇 |
1986年 | 31篇 |
1985年 | 52篇 |
1984年 | 51篇 |
1983年 | 28篇 |
1982年 | 47篇 |
1981年 | 49篇 |
1980年 | 79篇 |
1979年 | 51篇 |
1978年 | 51篇 |
1977年 | 38篇 |
1976年 | 32篇 |
1975年 | 49篇 |
1974年 | 41篇 |
1973年 | 47篇 |
1972年 | 33篇 |
1971年 | 35篇 |
1970年 | 32篇 |
1967年 | 27篇 |
1966年 | 23篇 |
排序方式: 共有2864条查询结果,搜索用时 15 毫秒
131.
132.
In a category with injective hulls and a cogenerator, the embeddings into injective hulls can never form a natural transformation,
unless all objects are injective. In particular, assigning to a field its algebraic closure, to a poset or Boolean algebra
its Mac-Neille completion, and to an R-module its injective envelope is not functorial, if one wants the respective embeddings to form a natural transformation.
Received January 21, 2000; accepted in final form August 10, 2001.
RID="h1"
RID="h2"
RID="h3"
ID="h1"The hospitality of York University is gratefully acknowledged by the first author.
ID="h2"Third author partially supported by the Grant Agency of the Czech Republic under Grant no. 201/99/0310, and the hospitality
of York University is also acknowledged.
ID="h3"Partial financial assistance by the Natural Sciences and Engineering Councel of Canada is acknowledged by the fourth
author. 相似文献
133.
Recent progress in the understanding of the high density phase of neutron stars advances the view that a substantial fraction of the matter consists of hyperons. The possible impacts of a highly attractive interaction between hyperons on the properties of compact stars are investigated. We find that a hadronic equation of state with hyperons allows for a first order phase transition to hyperonic matter. The corresponding hyperon stars can have rather small radii of R approximately equal 8 km. 相似文献
134.
Steffen Härtel Svitlana Tykhonova Marcus Haas Horst A. Diehl 《Journal of fluorescence》2002,12(3-4):465-479
Fluorescence spectroscopy and microscopy are powerful techniques to detect dynamic properties in artificial and natural lipid membrane systems. Unfortunately, most fluorescent dyes that sense dynamically relevant membrane parameters are UV sensitive. Their major disadvantage is a high susceptibility to fluorescence bleaching. Additionally, the risk for hazardous damages in biological components generally increases with decreasing excitation wavelength. Therefore the use of non-UV–sensitive membrane dyes would provide significant advantage, particularly for applications in fluorescence microscopy, which usually implies high local excitation intensities. We applied steady-state fluorescence spectroscopy techniques to several UV and non-UV membrane dyes to detect and compare dynamically relevant excitation and emission characteristics. Small unilamellar liposomes (composed of egg yolk phosphatidylcholine) served as a model system for biological membranes. The dynamic properties of the membranes were varied by two independent parameters: the intrinsic cholesterol content (0–50 mol%) and temperature (10–50°C). We tested four non-UV–sensitive membrane dyes: 9-diethylamino-5H-benzophenoxazine-5-one (Nile Red), 4-(dicyanovinyl)julolidine (DCVJ), N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl) pyridinium dibromide (FM 4-64), and 1,1-dioctadecyl-3,3,3,3-tetramethylindocarbocyanine perchlorate (DiIC18). We also tested three derivatives of DiIC18: DiIC16 and DiIC12 differ in acyl chain length and Fast-DiIC18 provides double bonds between hydrocarbon atoms. The spectral results were compared to established fluorescence characteristics of four UV membrane dyes: the anisotropy of 1-6-phenyl-1,3,5,-hexatrien (DPH), two derivatives of DPH (TMA-DPH and COO–-DHP), and the generalized polarization of 6-dodecanoyl-2-dimethyl-aminonaphthalene (Laurdan). Our results indicate that the tested non-UV dyes do not reveal dynamically relevant membrane parameters in a direct manner. However, spectral characteristics make DiIC18, Nile Red, and DCVJ promising probes for the microscopic detection of lateral lipid organization, an indirect indicator of membrane dynamics. In particular, DiIC18 showed very selective shifts in the emission spectra at defined temperatures and cholesterol contents that have not been reported elsewhere. 相似文献
135.
van der Horst R Leeuw AR Dreschler WA 《The Journal of the Acoustical Society of America》1999,105(3):1801-1809
The role of different modulation frequencies in the speech envelope were studied by means of the manipulation of vowel-consonant-vowel (VCV) syllables. The envelope of the signal was extracted from the speech and the fine-structure was replaced by speech-shaped noise. The temporal envelopes in every critical band of the speech signal were notch filtered in order to assess the relative importance of different modulation frequency regions between 0 and 20 Hz. For this purpose notch filters around three center frequencies (8, 12, and 16 Hz) with three different notch widths (4-, 8-, and 12-Hz wide) were used. These stimuli were used in a consonant-recognition task in which ten normal-hearing subjects participated, and their results were analyzed in terms of recognition scores. More qualitative information was obtained with a multidimensional scaling method (INDSCAL) and sequential information analysis (SINFA). Consonant recognition is very robust for the removal of certain modulation frequency areas. Only when a wide notch around 8 Hz is applied does the speech signal become heavily degraded. As expected, the voicing information is lost, while there are different effects on plosiveness and nasality. Even the smallest filtering has a substantial effect on the transfer of the plosiveness feature, while on the other hand, filtering out only the low-modulation frequencies has a substantial effect on the transfer of nasality cues. 相似文献
136.
Horst Kessler Günther Becker Herbert Kogler Michael Wolff 《Tetrahedron letters》1984,25(36):3971-3974
2-(2-pyridyl-)ethyl esters are used as chemically inert, highly selective protecting groups that are removable under mild conditions via a two step procedure. 相似文献
137.
Horst Thielemann 《Fresenius' Journal of Analytical Chemistry》1988,332(4):372
Ohne Zusammenfassung
Sorption layers impregnated with silver nitrate for the separation of polyhydric phenolic compounds相似文献
138.
Horst Tempelmeier 《European Journal of Operational Research》1985,19(3):313-323
In this paper an analytical model is presented which permits the determination of the minimal inventory reorder point subject to (a) a maximum specified expected customer order waiting time or (b) a maximum specified probability of a customer order waiting more than a predetermined time span. The probability distribution of the customer order waiting time is determined for an arbitrary demand distribution (e.g. normal, gamma or exponential) and under stochastic replenishment lead time conditions by use of arguments from renewal theory. The results established can be used for the customer-oriented control of inventory policy as well as for the analysis of multi-echelon inventory systems. 相似文献
139.
Ohne Zusammenfassung 相似文献
140.