全文获取类型
收费全文 | 11102篇 |
免费 | 932篇 |
国内免费 | 426篇 |
专业分类
系统科学 | 1496篇 |
丛书文集 | 178篇 |
教育与普及 | 91篇 |
理论与方法论 | 286篇 |
现状及发展 | 900篇 |
研究方法 | 8篇 |
综合类 | 9500篇 |
自然研究 | 1篇 |
出版年
2024年 | 31篇 |
2023年 | 87篇 |
2022年 | 158篇 |
2021年 | 190篇 |
2020年 | 156篇 |
2019年 | 112篇 |
2018年 | 868篇 |
2017年 | 885篇 |
2016年 | 594篇 |
2015年 | 341篇 |
2014年 | 385篇 |
2013年 | 420篇 |
2012年 | 707篇 |
2011年 | 1371篇 |
2010年 | 1214篇 |
2009年 | 854篇 |
2008年 | 916篇 |
2007年 | 1096篇 |
2006年 | 287篇 |
2005年 | 241篇 |
2004年 | 293篇 |
2003年 | 279篇 |
2002年 | 220篇 |
2001年 | 154篇 |
2000年 | 120篇 |
1999年 | 75篇 |
1998年 | 45篇 |
1997年 | 55篇 |
1996年 | 30篇 |
1995年 | 42篇 |
1994年 | 46篇 |
1993年 | 29篇 |
1992年 | 32篇 |
1991年 | 39篇 |
1990年 | 31篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1967年 | 1篇 |
1960年 | 1篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Doug Walton 《Systemic Practice and Action Research》2007,20(5):369-386
Public discourse in Western democracies, particularly in the United States, is far from the Habermasian ideal of citizens
engaging in a rational discussion of public affairs. Rather than providing an arena for informed deliberation, the growing
expertise of the media, lobbyists, and politicians has sub-optimized the current system of discourse to focus on emotional
manipulation and the creation of polarized interests, each competing with each other for dominance. Avoiding a potentially
disastrous outcome from this unbalancing of public discourse requires a revitalization of the public sphere and a return of
the citizen voice in public decision making. To that end, systems thinkers have a tremendous opportunity and can play an important
role. This article will explore the current challenges facing public discourse and outline that potential role. 相似文献
962.
Ten terminal or subterminal RFLP markers belonging to linkage groups 1, 3, 5, 6, and 10 in maize RFLP map were physically
locted onto maize mitotic chromosomes with in situ hybridization. All biotinylated probes from 600 to 2 250 bp were detected
by DAB staining. The markers belonging to linkage groups 1, 3, 5, 6, and 10 correspondingly located at the chromosomes 1,
3, 5, 6, and 10. All of the tested markers except bnl6.25 and umc44 were duplicated sequences. Each of them was also labeled
on another chromosome besides on the chromosome corresponding to its linkage group. The marker bnl3. 04 was triplicated sequences
and the signals were detected on three nonhomologous chromosomes. In the tested ten markers, there were only four located
at the ends of corresponding chromosomes. Others were located at sites midway along the chromosome arms or near the centromeres.
The region covered by two terminal or subterminal markers in each of linkage groups 1, 3, 5, and 6 occupied 80.02%, 38.25%,
82.30% and 51.16% of the region of both short and long arms in chromosomes 1, 3, 5, and 6 respectively. Only two terminal
markers of linkage group 10 covered the whole chromosome 10. In some linkage groups, two terminal or subterminal markers covered
a short genetic distance but were physically distant, while two covering a longer genetic distance were physically closer.
Supported by The National Natural Science Foundation of China and the Doctorate Vesting Point Foundation of the Education
Committec of the People's Republic of China
Mao Ninghui: born in 1986, used to be an MS student of Wuhan University in 1992–1995 and now is working in Fudan University,
Shanghai 200433 相似文献
963.
XIA Yingqing TIAN Huamei DUAN Zhiguo WU Ling XU Penggen 《武汉大学学报:自然科学英文版》2007,12(3):481-484
This paper presents a method to analyze and calculate the angular glint of targets. By parting the target to very small size cells, using high-frequency approximation, the near-field radar cross section (RCS) is calculated based on the scattering from complex targets and environments (SCTE) system, and the angular glint is calculated by the phase grads. The results show that the angular glint can be calculated exactly in the SCTE system, and this method is correct and efficient. In the near-zone, the far-field theory is not applicable and the angular glint should be calculated by the near-field theory. 相似文献
964.
TAN Zuowen 《武汉大学学报:自然科学英文版》2008,13(6):680-684
A group-oriented (t, n) threshold signature scheme employs the cryptographic techniques of secret share, allows any subset of t players out of n players to sign message on behalf of the group and disallows the creation of a valid signature if fewer than t players take part in the signature protocol. In this paper, we proposed a new group-oriented (t, n) threshold signature schemes with traceable signers based on Schnorr signature. The proposed scheme is proved traceable, robust and unforgeable against the "static" adversary with the discrete logarithm assumption in the random oracle model and existence of broadcast channel. The proofs of the strongest security (existential unforgeability against adaptively chosen message attacks under the discrete logarithm assumption) are provided in the random oracle model. 相似文献
965.
Traditional approach of design by contract, due to mixing the contract code with application code, is difficult for the extensibility
and reusability of software system. This paper presents a framework named JADBC for design by contract based on Aspect-Oriented
Programming (AOP) to resolve these problems. By providing a new modularized element, aspect, the framework successfully separates
the contracts in design by contract, from functional codes. The implementation of this framework is based on dynamic AOP which
can have the contract changed at runtime, consequently, enhancing program flexibility. JADBC framework modularizes the contracts
in a clear-cut fashion that is easier to design, implement, and maintain.
Biography: WEN Jing (1982–), female, Ph.D. candidate, research directions: software engineer, aspect-oriented software development. 相似文献
966.
李超 《莆田高等专科学校学报》2008,(3):69-71
隋树森编的《全元散曲》作为散曲研究的材料很完备,但在使用过程中发现其中仍有诸如断句、脱韵、字词讹误、次序颠倒等等不少疏失之处,试依据曲律、曲韵对其中的字句脱漏、讹误、颠倒及其他一些讹误进行校勘,以期为研究者提供些参考。 相似文献
967.
CHEN Lihua 《武汉大学学报:自然科学英文版》2008,13(1):9-13
The singularly perturbed initial boundary value problems for the reaction diffusion system are raised. Firstly, under suitable conditions, using a iteration technique, the differential inequalities theorem is constructed and introducing two auxiliary functions the existence and uniqueness theorem of solution for the basic reaction diffusion system is proved. Using the singularly perturbed method the formal asymptotic expressions of the solution are constructed with power series theory. By using the comparison theorem the existence and its asymptotic behavior of solution for the original problem are studied. Finally, using method of estimate inequalities, the structure of solutions for the problem is discussed thoroughly in three cases and asymptotic solution of the original problem is given. The asymptotic behavior of solution in the three cases is proved. 相似文献
968.
马朝东 《西安联合大学学报》2008,11(1):54-56
“胸有成竹”与“心手相应”是文同提出的两种绘画思想,亦适合于书法。这两种思想展示了从观察到构思、再到表现这一艺术创作的主要环节和基本过程。它们的关系是相辅相成、互相作用、缺一不可的。艺与艺通,艺中有道;技进乎道,乃臻至境。 相似文献
969.
针对在强干扰背景中检测弱目标信号时被动声信号处理技术的性能会严重降低的问题,提出了一种自适应空域矩阵滤波器的设计方法。该方法是在保证滤波器通带响应与期望响应误差和阻带响应低于某设定值的条件下,最小化滤波后基阵的输出功率,使得滤波器能尽量保证让通带扇面的信号无失真通过,同时抑制阻带扇面的干扰和噪声。将滤波器的优化设计问题表达成二阶锥规划的形式,利用已有的内点方求出其数值解。最后将设计的自适应空域矩阵滤波器用于强干扰背景中弱目标信号的方位估计。计算机仿真结果说明,所提方法能在干扰方位形成零陷,有效地抑制阻带区域的强干扰,提高了后续方位估计方法的性能。 相似文献
970.
OPTIMAL MAINTENANCE AND REPLACEMENT OF EXTRACTION MACHINERY 总被引:1,自引:1,他引:0
This paper considers a problem of optimal preventive maintenance and replacement schedule of equipment devoted to extracting resources from known deposits. Typical examples are oil drills, mine shovels, etc. At most one replacement of the existing machinery by a new one is allowed. The problem is formulated as an optimal control problem subject to the state constraint that the remaining deposit at any given time is nonnegative. We show that the optimal preventive maintenance, production rates, and the replacement and salvage times of the existing machinery and the new one, if required, can be obtained by solving sequentially a series of free-end-point optimal control problems. Moreover, an algorithm based on this result is developed and used to solve two illustrative examples. 相似文献