全文获取类型
收费全文 | 10310篇 |
免费 | 845篇 |
国内免费 | 208篇 |
专业分类
系统科学 | 1292篇 |
丛书文集 | 114篇 |
教育与普及 | 72篇 |
理论与方法论 | 293篇 |
现状及发展 | 891篇 |
研究方法 | 12篇 |
综合类 | 8688篇 |
自然研究 | 1篇 |
出版年
2024年 | 21篇 |
2023年 | 41篇 |
2022年 | 97篇 |
2021年 | 97篇 |
2020年 | 89篇 |
2019年 | 35篇 |
2018年 | 779篇 |
2017年 | 788篇 |
2016年 | 502篇 |
2015年 | 165篇 |
2014年 | 199篇 |
2013年 | 187篇 |
2012年 | 495篇 |
2011年 | 1183篇 |
2010年 | 1046篇 |
2009年 | 696篇 |
2008年 | 788篇 |
2007年 | 1013篇 |
2006年 | 255篇 |
2005年 | 258篇 |
2004年 | 282篇 |
2003年 | 280篇 |
2002年 | 208篇 |
2001年 | 162篇 |
2000年 | 123篇 |
1999年 | 224篇 |
1998年 | 162篇 |
1997年 | 172篇 |
1996年 | 137篇 |
1995年 | 151篇 |
1994年 | 138篇 |
1993年 | 93篇 |
1992年 | 103篇 |
1991年 | 73篇 |
1990年 | 70篇 |
1989年 | 74篇 |
1988年 | 76篇 |
1987年 | 42篇 |
1986年 | 41篇 |
1985年 | 15篇 |
1983年 | 1篇 |
1967年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 55 毫秒
991.
A new generation of cement, microbe cement, has been developed in response to the ever increasing awareness of environmental protection. Microbe cement is a new strengthening material based on microbiologically induced precipitation of calcium carbonate. This paper confirms the feasibility of binding loose sand particles using microbe cement and details the cementation mechanism of microbe cement. We have also prepared microbe cementitious materials (biosandstones). The compressive strength of the bio-sandstone, which depends on the content of calcium carbonate produced by microbially induced precipitation and the bio-mediated calcite crystal size, could be up to 12 MPa at an age of 20 days. By increasing the precipitated calcite content, the compressive strength and microstructure of bio-sandstone could be improved. 相似文献
992.
K-means clustering is arguably the most popular technique for partitioning data. Unfortunately, K-means suffers from the well-known
problem of locally optimal solutions. Furthermore, the final partition is dependent upon the initial configuration, making
the choice of starting partitions all the more important. This paper evaluates 12 procedures proposed in the literature and
provides recommendations for best practices. 相似文献
993.
This paper presents a fast pseudorandom generation algorithm, which is based on the BLAKE hash function and can pass the random
test of the NIST (National Institute of Standards and Technology) Statistical Test Suite. Through theoretical analysis and
experimental imitation, our new algorithm is proven to be more secure and efficient than G-SHA1. Simultaneously, we introduce
and discuss the BLAKE in detail. Its security shows that can be utilized to generate pseudorandom bit sequences, which the
experimental results show the BLAKE hash function has excellent pseudorandomness. Therefore, we believe the BLAKE is one of
the most potential candidate algorithms of SHA-3 program. 相似文献
994.
NECESSARY AND SUFFICIENT CONDITION FOR GLOBAL CONTROLLABILITY OF A CLASS OF AFFINE NONLINEAR SYSTEMS
Yimin SUN Shengwei MEI Qiang LU 《系统科学与复杂性》2007,20(4):492-500
In this paper, we investigate the global controllability of a class of n-dimensional affine nonlinear systems with n- 1 controls and constant control matrix. A necessary and sufficient condition for its global controllability has been obtained by using the methods recently developed. Furthermore, we generalize the above result to a class of affine nonlinear systems with a block-triangular-like structure. Finally, we will give three examples to show the applications of our results. 相似文献
995.
This paper gives a theoretical analysis for the algorithms to compute functional decomposition for multivariate polynomials based on differentiation and homogenization which were proposed by Ye,Dai,and Lam(1999) and were developed by Faugere,Perret(2006,2008,2009).The authors show that a degree proper functional decomposition for a set of randomly decomposable quartic homogenous polynomials can be computed using the algorithm with high probability.This solves a conjecture proposed by Ye,Dai,and Lam(1999).The authors also propose a conjecture which asserts that the decomposition for a set of polynomials can be computed from that of its homogenization and show that the conjecture is valid with high probability for quartic polynomials.Finally,the authors prove that the right decomposition factors for a set of polynomials can be computed from its right decomposition factor space. 相似文献
996.
从邻氯苯酚出发合成邻氯苯氧乙酰异硫氯氰酸酯,分别与5种2-氨基-5-芳基-1,3,4-恶二反应得到1,3,4-恶二唑的邻氯苯氧乙酰基硫脲衍生物,用IR,^1HNMR,元素分析等对它们的结构进行了确证,并分析归纳合成该目标产物的最佳合成条件。 相似文献
997.
998.
999.
通过对苹果香气成分的离析方法(顶空法、蒸馏法、萃取法等)进行对比性研究,确定改进的Likens&Nickerson蒸馏萃取法适合于普通毛细管气相色谱仪的分析条件,是一种良好的方法 相似文献
1000.
叶芳草 《厦门大学学报(自然科学版)》1989,28(4):337-342
文中给出第Ⅰ类型的 7种非例外、不可约、大范围的Riemann对称空间R~1上的在其可递的解析变换群(运动群)下不变的微分算子集合 D(R~1)的一组基或求此基的方法。 相似文献