全文获取类型
收费全文 | 5922篇 |
免费 | 406篇 |
国内免费 | 1563篇 |
出版年
2024年 | 5篇 |
2023年 | 85篇 |
2022年 | 112篇 |
2021年 | 154篇 |
2020年 | 151篇 |
2019年 | 279篇 |
2018年 | 236篇 |
2017年 | 228篇 |
2016年 | 213篇 |
2015年 | 274篇 |
2014年 | 310篇 |
2013年 | 418篇 |
2012年 | 419篇 |
2011年 | 399篇 |
2010年 | 274篇 |
2009年 | 393篇 |
2008年 | 391篇 |
2007年 | 422篇 |
2006年 | 384篇 |
2005年 | 356篇 |
2004年 | 312篇 |
2003年 | 308篇 |
2002年 | 307篇 |
2001年 | 206篇 |
2000年 | 208篇 |
1999年 | 183篇 |
1998年 | 122篇 |
1997年 | 77篇 |
1996年 | 109篇 |
1995年 | 131篇 |
1994年 | 83篇 |
1993年 | 65篇 |
1992年 | 57篇 |
1991年 | 44篇 |
1990年 | 32篇 |
1989年 | 25篇 |
1988年 | 21篇 |
1987年 | 23篇 |
1986年 | 15篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 15篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有7891条查询结果,搜索用时 50 毫秒
22.
Understanding the state of forest resource utilization in China and correctly evaluating the role and function of forest resources in national economic development are essential for realizing balanced development of forests, the environment, and the economy. This is especially true given the present situation of increasingly scarce forest resources. Using data from Chinese forest industry statistical yearbooks, forestry development reports, and other documents, this paper examines the current state of forest resource utilization in China from the angle of combining quantities and values based on input–output tables. We show that demand for and input use of forest resources varies greatly across industrial sectors; the paper products and furniture manufacturing industries have the greatest direct consumption coefficient for timber use. When considering direct and indirect demand, it is clear that forest resources restrict different industrial sectors in diverse ways. These results provide an important set of reference values regarding the utilization of forest resources and coordinated industrial development in China. 相似文献
23.
24.
Effect of Asahi SL on China aster ‘Aleksandra’ seed yield, germination and some metabolic events 总被引:2,自引:0,他引:2
The effects of Asahi SL (sodium ortho and para-nitro phenolate, sodium 5 nitro guaiacolate) sprays on China aster plant height,
seed yield and some metabolic events were investigated. The plants were sprayed with Asahi SL, in concentration of 0, 0.1,
0.2 or 0.4 %, three times before or during flowering, and six times before and during this stage. It was found that Asahi
SL applied three times during flowering brought about an increase in the seed yield, germination and metabolic activity and
did not modify vegetative growth of plants. The chemical used earlier, before flowering, had detrimental effect on seed yield
and quality, although it stimulated vegetative growth. The positive effect of Asahi SL was more prominent in weather conditions
unfavourable for seed production. 相似文献
25.
26.
Paederus jianyueae Peng & Li, sp. n. (Zhejiang: Qingliangfeng) is described and illustrated. Additional records of P. biacutus Li, Zhou & Solodovnikov, 2014 and P. parvidenticulatus Li, Zhou & Solodovnikov, 2014 are reported. 相似文献
27.
The genus Primeuchroeus Linsenmaier, 1968 from China is revised and an illustrated identification key is produced for the first time. Three species are recorded from China, with one species, Primeuchroeus yongdaerianus Kim, new to China. 相似文献
28.
29.
The spectra of k-mer frequencies can reveal the structures and evolution of genome sequences. We confirmed that the trimodal spectrum of 8-mers in human genome sequences is distinguished only by CG2, CG1 and CG0 8-mer sets, containing 2,1 or 0 CpG, respectively. This phenomenon is called independent selection law. The three types of CG 8-mers were considered as different functional elements. We conjectured that (1) nucleosome binding motifs are mainly characterized by CG1 8-mers and (2) the core structural units of CpG island sequences are predominantly characterized by CG2 8-mers. To validate our conjectures, nucleosome occupied sequences and CGI sequences were extracted, then the sequence parameters were constructed through the information of the three CG 8-mer sets respectively. ROC analysis showed that CG1 8-mers are more preference in nucleosome occupied segments (AUC > 0.7) and CG2 8-mers are more preference in CGI sequences (AUC > 0.99). This validates our conjecture in principle. 相似文献
30.