全文获取类型
收费全文 | 83669篇 |
免费 | 4688篇 |
国内免费 | 56篇 |
专业分类
林业 | 2911篇 |
农学 | 2276篇 |
基础科学 | 563篇 |
9190篇 | |
综合类 | 14874篇 |
农作物 | 3083篇 |
水产渔业 | 3896篇 |
畜牧兽医 | 45683篇 |
园艺 | 879篇 |
植物保护 | 5058篇 |
出版年
2018年 | 1032篇 |
2017年 | 1170篇 |
2016年 | 1087篇 |
2015年 | 935篇 |
2014年 | 1172篇 |
2013年 | 3052篇 |
2012年 | 2122篇 |
2011年 | 2697篇 |
2010年 | 1652篇 |
2009年 | 1754篇 |
2008年 | 2591篇 |
2007年 | 2402篇 |
2006年 | 2403篇 |
2005年 | 2127篇 |
2004年 | 2089篇 |
2003年 | 2076篇 |
2002年 | 1969篇 |
2001年 | 2700篇 |
2000年 | 2803篇 |
1999年 | 2132篇 |
1998年 | 813篇 |
1997年 | 823篇 |
1996年 | 807篇 |
1995年 | 1017篇 |
1994年 | 889篇 |
1993年 | 841篇 |
1992年 | 1930篇 |
1991年 | 2081篇 |
1990年 | 1924篇 |
1989年 | 1936篇 |
1988年 | 1826篇 |
1987年 | 1930篇 |
1986年 | 1977篇 |
1985年 | 1874篇 |
1984年 | 1481篇 |
1983年 | 1298篇 |
1982年 | 880篇 |
1979年 | 1368篇 |
1978年 | 1124篇 |
1977年 | 973篇 |
1976年 | 937篇 |
1975年 | 983篇 |
1974年 | 1272篇 |
1973年 | 1298篇 |
1972年 | 1235篇 |
1971年 | 1147篇 |
1970年 | 1088篇 |
1969年 | 965篇 |
1968年 | 832篇 |
1967年 | 869篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
182.
Gingerich PD 《Science (New York, N.Y.)》1983,222(4620):159-161
Rates of morphological evolution documented in laboratory selection experiments, historical colonization events, and the fossil record are inversely related to the interval of time over which they are measured. This inverse relationship is an artifact of comparing a narrow range of morphological variation over a wide range of time intervals, and it is also a product of time averaging. Rates measured over different intervals of time must be scaled against interval length before they can be compared. 相似文献
183.
184.
185.
186.
187.
188.
Blackmore DK 《New Zealand veterinary journal》1983,31(10):167-169
189.
190.
Knowlen GG Kittleson MD Nachreiner RF Eyster GE 《Journal of the American Veterinary Medical Association》1983,183(9):991-996
The plasma aldosterone concentration (PAC) among clinical status groups of 23 dogs with chronic heart failure was compared at various times after diagnosis of the problem. Eighteen dogs admitted in New York Heart Association (NYHA) class IV clinical status had significant elevations in PAC (P<0.0001), when compared with clinically normal dogs. Five dogs admitted in NYHA class III status and 4 dogs that responded with a change to NYHA class III status had significant elevations in PAC (P<0.01), when compared with clinically normal dogs. In patients with NYHA class IV status, the PAC was significantly greater (P<0.01) than in patients in NYHA class III status. For patients with the poorest prognosis, ie, severe signs of NYHA class IV status, the PAC was not markedly different, when compared with that for patients with a favorable prognosis, ie, recent onset of signs of NYHA class IV status. Patients treated with captopril had significantly lower PAC after therapy (P<0.01), whereas patients treated with hydralazine had significantly higher PAC (P<0.05) after therapy. It was concluded that heart failure in the dog increases PAC, most likely because of renin-angiotensin-aldosterone-system activation, and that the increase is related directly to the clinical status of the patient. Further, it was concluded that treatment of dogs in heart failure with captopril causes a decrease in circulating PAC, whereas treatment with hydralazine causes an increase in circulating PAC. 相似文献