全文获取类型
收费全文 | 838822篇 |
免费 | 99419篇 |
国内免费 | 359篇 |
专业分类
938600篇 |
出版年
2016年 | 9206篇 |
2015年 | 12721篇 |
2014年 | 15059篇 |
2013年 | 21924篇 |
2012年 | 24407篇 |
2011年 | 24603篇 |
2010年 | 16403篇 |
2009年 | 15399篇 |
2008年 | 22083篇 |
2007年 | 22876篇 |
2006年 | 21651篇 |
2005年 | 20831篇 |
2004年 | 20650篇 |
2003年 | 19873篇 |
2002年 | 19312篇 |
2001年 | 36054篇 |
2000年 | 36679篇 |
1999年 | 29425篇 |
1998年 | 10775篇 |
1997年 | 11360篇 |
1996年 | 10931篇 |
1995年 | 10259篇 |
1994年 | 10304篇 |
1993年 | 10185篇 |
1992年 | 25472篇 |
1991年 | 25032篇 |
1990年 | 24689篇 |
1989年 | 24247篇 |
1988年 | 22340篇 |
1987年 | 21499篇 |
1986年 | 20065篇 |
1985年 | 20306篇 |
1984年 | 16902篇 |
1983年 | 14859篇 |
1982年 | 11447篇 |
1981年 | 10541篇 |
1980年 | 10028篇 |
1979年 | 16684篇 |
1978年 | 12999篇 |
1977年 | 11857篇 |
1976年 | 11348篇 |
1975年 | 12463篇 |
1974年 | 13063篇 |
1973年 | 12862篇 |
1972年 | 12010篇 |
1971年 | 10559篇 |
1970年 | 9265篇 |
1969年 | 8700篇 |
1968年 | 7957篇 |
1967年 | 7018篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
912.
913.
914.
915.
916.
917.
918.
Fire has historically been an important ecological component of forests in the Intermountain Region of the northwestern United States. This study is set in a small biogeographically disjunct mountain range. Our research objectives were to (1) investigate the historical frequency, severity, size, and spatial pattern of fire; (2) determine if and how fire regimes have changed since Euro-American settlement; and (3) compare how fire regimes of a small isolated range compare to nearby, but considerably larger, mountain agglomerations. Our findings suggest that this mountain range has historically supported fires typified by small size and high frequency, resulting in a high degree of spatial pattern complexity compared to mountain agglomerations. We also found disparity in size and burn severity solely within the study area based on the bisecting Continental Divide. Since the advent of Euro-American settlement in the 1870s, fire frequency and sizes of individual fires in the West Big Hole Range have significantly decreased resulting in an estimated 87% reduction in area burned. We discuss potential relationships of mountain range isolation and fire regimes in the Intermountain Region. Furthermore, we suggest that the relative small size of this mountain range predisposes it to greater anthropogenic effects upon fire occurrence. 相似文献
919.
920.
V T Kondakov A B Okulov M A Filippkin R Z Tandilava I U Artamonov O A Voronenko A N Sazonov 《Vestnik rentgenologii i radiologii》1991,(4):31-35
The paper is concerned with analysis of the results of intraoperative phlebotesticulography, performed in 50 patients with varicocele of degree I-II during Ivanissevich's operation. The effect of surgical intervention was shown to depend upon the quality of ligation of the testicular vein, some parts of which are anastomosed between themselves. The localization of this anastomosis is revealed by means of intraoperative phlebotesticulography, which permits increasing the results of surgical treatment and predicting a course of a postoperative period. 相似文献