全文获取类型
收费全文 | 15665篇 |
免费 | 833篇 |
国内免费 | 534篇 |
专业分类
系统科学 | 1399篇 |
丛书文集 | 354篇 |
教育与普及 | 290篇 |
理论与方法论 | 307篇 |
现状及发展 | 924篇 |
研究方法 | 44篇 |
综合类 | 13710篇 |
自然研究 | 4篇 |
出版年
2024年 | 67篇 |
2023年 | 124篇 |
2022年 | 193篇 |
2021年 | 220篇 |
2020年 | 106篇 |
2019年 | 43篇 |
2018年 | 787篇 |
2017年 | 817篇 |
2016年 | 515篇 |
2015年 | 260篇 |
2014年 | 347篇 |
2013年 | 287篇 |
2012年 | 553篇 |
2011年 | 1286篇 |
2010年 | 1134篇 |
2009年 | 803篇 |
2008年 | 944篇 |
2007年 | 1185篇 |
2006年 | 373篇 |
2005年 | 418篇 |
2004年 | 420篇 |
2003年 | 376篇 |
2002年 | 317篇 |
2001年 | 279篇 |
2000年 | 305篇 |
1999年 | 570篇 |
1998年 | 565篇 |
1997年 | 570篇 |
1996年 | 518篇 |
1995年 | 450篇 |
1994年 | 403篇 |
1993年 | 317篇 |
1992年 | 311篇 |
1991年 | 297篇 |
1990年 | 219篇 |
1989年 | 237篇 |
1988年 | 183篇 |
1987年 | 123篇 |
1986年 | 65篇 |
1985年 | 17篇 |
1984年 | 6篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1969年 | 4篇 |
1967年 | 3篇 |
1964年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
921.
Langevin equation is widely used to study the stochastic effects in molecular networks, as it often approximates well the
underlying chemical master equation. However, frequently it is not clear when such an approximation is applicable and when
it breaks down. This paper studies the simple Schnakenberg model consisting of three reversible reactions and two molecular
species whose concentrations vary. To reduce the residual errors from the conventional formulation of the Langevin equation,
the authors propose to explicitly model the effective coupling between macroscopic concentrations of different molecular species.
The results show that this formulation is effective in correcting residual errors from the original uncoupled Langevin equation
and can approximate the underlying chemical master equation very accurately. 相似文献
922.
For liquid Ti, it is difficult to achieve high undercooling because of its chemical reactivity; as a result, there is little information available on its properties and structure in the undercooled state. In this study, we investigate the density and structure, using molecular dynamics method, for the undercooling and superheating ranges 0-743 K and 0-457 K. The density increases quadratically for undercooling. At the melting temperature, the density is 4.14 g/cm3, and first and second temperature coefficients are obtained. The pair correlation functions and coordination numbers indicate that the short range degree of order becomes increasingly significant with increasing undercooling. 相似文献
923.
A box model of the interhemispheric thermohaline circulation (THC) in atmosphere-ocean for global climate is considered. By
using the generalized variational iteration method, the approximate solution of a simplified nonlinear model is studied. The
generalized variational iteration method is an analytic method, and the obtained analytic solution can be operated sequentially.
The authors also diversify qualitative and quantitative behaviors for corresponding physical quantities. 相似文献
924.
Diatom oxygen isotopes have been widely applied in quantitative reconstruction of the paleoclimate and paleoenvironment, but
have rarely been reported in China. In the present study, Lake Sihailongwan in Northeast China was selected for detailed investigation
of oxygen isotopic fractionation between diatom frustules and lake water induced by growth temperature. This study involved
a 2-year period of field monitoring of the lake water temperature at multiple depths and biweekly collections of traps for
both sediment and water at shallow and bottom depths (7 and 49 m below the lake surface, respectively), diatom separation
and purification of the trap sediments, and oxygen isotope measurement for diatom silica and lake water samples. The conditioned
experiment conducted herein demonstrated that the laboratory device, methods and techniques used in this study were capable
of generating reliable data for the typical oxygen isotope composition of diatom frustules. The data obtained revealed a prominent
linear relationship between the oxygen isotope composition of the modern diatom and lake temperature during growth. The fractionation
coefficient was about −0.185‰/°C−0.238‰/°C in the temperature range of 3.6–24°C, which is consistent with the observations
from various aquatic environments and laboratory culture with different diatom taxa. These findings provide strong support
for the dominant control of the growth temperature on the oxygen isotope fractionation between the diatom frustules and ambient
water. A notable difference in the fractionation coefficient was observed between the surface and bottom diatom oxygen isotopes,
suggesting that various depositional processes and taphonomic effects influenced the surface and bottom trap samples. Another
factor leading to this difference may be that enrichment by evaporation and dilution by rainfall have a stronger influence
on the surface. Overall, the results presented here demonstrate significant progress in evaluation of diatom oxygen isotopes
in China and draw attention to the differences between surface and bottom diatom oxygen isotope compositions. 相似文献
925.
A surface plasmon resonance (SPR) technique was developed as an online screening method to identify effective adsorbents for the peptide NH2-Cys-Thr-Trp-Trp-COOH (CW-4). To validate the SPR technique, several linear polymers containing amino acid residues were synthesized as models of their corresponding adsorbents. SPR screening of all the linear polymers demonstrated that the linear polymer containing phenylalanine residues (PPhe) exhibited the highest affinity for CW-4 among the polymers tested. In accordance with the screening results from SPR, the adsorbent containing phenylalanine (APhe) exhibited the highest adsorption capacity for CW-4. An interesting observation was that the amounts of CW-4 adsorbed on 3 adsorbents were quite small, even though both SPR and isothermal titration calorimetry (ITC) experiments indicated the presence of interactions between CW-4 and the three polymers. A kinetic analysis performed using SPR technology suggested such a phenomenon was ascribed to the poor stability of the CW-4/polymer complexes; that is, CW-4 associates with the polymers quickly, but it also dissociated quickly. The combined results suggested that SPR was a promising tool to identify the optimal adsorbent for peptides, analyze the interactions contributing to adsorption and explain adsorption phenomena using polymer models. 相似文献
926.
927.
依据我国的资源、环境、技术条件及现有基础,分析了特色养殖业的风险性及适宜我国各地区养殖的品种,提出了建议性饲养管理模式。 相似文献
928.
石油化工装置设计与安全 总被引:6,自引:0,他引:6
针对石油化工装置中存在的危险因素,从工艺设计、装置布置设计、工艺管道设计、设计缺陷防范等多方面详细介绍保证石油化工装置安全的设计方法和措施,强调了安全设计的重要性。 相似文献
929.
930.
孙成科 《曲靖师范学院学报》2009,28(3)
针对结构化学教学中经常遇到的一些十分重要又较难理解、模糊不清的基本概念进行介绍和讨论。这些概念甚至在一些化学教材中也经常混淆不清. 相似文献