全文获取类型
收费全文 | 60363篇 |
免费 | 5949篇 |
国内免费 | 4861篇 |
专业分类
林业 | 4762篇 |
农学 | 5602篇 |
基础科学 | 3322篇 |
8250篇 | |
综合类 | 20807篇 |
农作物 | 3831篇 |
水产渔业 | 4887篇 |
畜牧兽医 | 12851篇 |
园艺 | 2681篇 |
植物保护 | 4180篇 |
出版年
2024年 | 299篇 |
2023年 | 785篇 |
2022年 | 1884篇 |
2021年 | 2306篇 |
2020年 | 2451篇 |
2019年 | 3047篇 |
2018年 | 2315篇 |
2017年 | 3204篇 |
2016年 | 2743篇 |
2015年 | 3300篇 |
2014年 | 3423篇 |
2013年 | 4120篇 |
2012年 | 4652篇 |
2011年 | 5120篇 |
2010年 | 4706篇 |
2009年 | 3822篇 |
2008年 | 3917篇 |
2007年 | 3426篇 |
2006年 | 2796篇 |
2005年 | 2231篇 |
2004年 | 1445篇 |
2003年 | 1243篇 |
2002年 | 1444篇 |
2001年 | 1221篇 |
2000年 | 1083篇 |
1999年 | 701篇 |
1998年 | 446篇 |
1997年 | 375篇 |
1996年 | 296篇 |
1995年 | 285篇 |
1994年 | 262篇 |
1993年 | 247篇 |
1992年 | 212篇 |
1991年 | 195篇 |
1990年 | 194篇 |
1989年 | 181篇 |
1988年 | 114篇 |
1987年 | 93篇 |
1986年 | 50篇 |
1985年 | 52篇 |
1984年 | 39篇 |
1983年 | 38篇 |
1982年 | 21篇 |
1981年 | 33篇 |
1978年 | 28篇 |
1977年 | 26篇 |
1976年 | 29篇 |
1974年 | 22篇 |
1973年 | 23篇 |
1972年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
5月22日,备受行业内关注的山东五征集团山拖农机装备有限公司揭牌仪式在山东省兖州市举行.至此,中国两大农机巨头--五征集团和山拖农装真正实现了战略性联合.见证了建国初期农机艰苦创业和改革开放后市场经济激烈竞争的山拖农装,遍尝辉煌与低谷的洗礼,在历经半世纪的风雨后,凤凰涅檠,浴火重生. 相似文献
5.
张微 《农业图书情报学刊》2009,21(11):143-145,149
从字迹是视觉信号这个角度来说,中小学生写字时最好使用较软质的铅笔或用钢笔。如果说低头歪头写字达不到书写"三个一"的要求,是孩子们"喜欢低头歪头",那么众多家庭从孩子小的时候就手把手地教孩子怎样握笔写字、上学后老师又是那么耐心地教学生如何正确执笔书写,反而还有如此多的学生还是很难达到书写"三个一"的要求呢? 相似文献
6.
7.
我代表中国奶业协会秘书处向各位理事、各位代表报告一年来工作情况,并对明年重点工作提出安排意见,请审议。 相似文献
8.
The cervical patency of six domestic female cats was monitored under sedation by infusion of contrast medium (Omnipaque) into the cranial vagina during early oestrus, mid‐oestrus, late oestrus and interoestrus or a radiopharmaceutical (99mTc‐HSA) during mid‐ and interoestrus in a non‐ovulatory oestrous cycle. The transport of the contrast medium or the radiopharmaceutical through the cervix and within the uterine horns was observed under fluoroscopy and with the aid of scintigraphy. In three of the queens, transcervical transport of contrast medium was demonstrated in all stages of oestrus, in one queen during mid‐oestrus, late oestrus and 1 day after oestrus, and in two queens only during late oestrus. The relations between the cervical patency to the contrast medium and the oestrous behaviour, cornification of the vaginal cells and the serum oestradiol‐17β concentration were evaluated, and a relationship was found between the cervical patency and the degree of vaginal cornification. Transcervical transport of the radiopharmaceutical was observed in three queens during mid‐oestrus. When the cervix was open, hysterography under a fluoroscope and hysteroscintigraphy were performed. The fluoroscopic and scintigraphic recordings revealed the patterns of the uterine contractions during oestrus in both ascending and descending directions, and the movement of the uterine contents back and forth between the uterine horns. The hysterograms were classified according to the shape of the uterine horns and the appearance of the endometrial lining. Spiral‐shaped uterine horns with a smooth inner contour were observed in two queens, and a corkscrew appearance with irregular filling defects in the uterine lumen was shown in two queens that had developed subclinical cystic endometrial hyperplasia. These findings demonstrated that fluids or particles deposited in the cranial vagina of the cat can be transported into the uterus during some stages of the oestrous cycle. The fluoroscopic and scintigraphic techniques developed in this study may be further modified to permit more detailed studies of uterine contractile patterns and sperm transport in the feline female reproductive tract. Hysterography proved useful to diagnose uterine disease. The information on cervical patency is of value also for the development of techniques for artificial insemination in this species, and should be studied also in the ovulatory cycle. 相似文献
9.
10.
Abstract – The different reproductive roles of the sexes can predict the direction and magnitude of sexual dimorphism of external and internal morphology. Males should have enlarged structures that enhance the acquisition of mating opportunities, whereas females are predicted to have enlarged organs that are associated with the production of eggs. We tested these predictions in male and female lake whitefish, a species in which both sexes have similar overall body size and shape. After controlling for body size, male lake whitefish had significantly longer jaws and pectoral and pelvic fins, larger hearts, and more muscle than females. Sexual dimorphism in relative muscle mass may be one of the most fundamental morphological differences between males and females. Females had relatively heavier livers than males. Because the liver is important for the breakdown of fats and vitellogenesis, selection should favour an enlarged liver in females for the processing of energy and the production of large numbers of eggs. 相似文献