全文获取类型
收费全文 | 254114篇 |
免费 | 14839篇 |
国内免费 | 651篇 |
专业分类
林业 | 23400篇 |
农学 | 13981篇 |
基础科学 | 2946篇 |
42633篇 | |
综合类 | 25311篇 |
农作物 | 17182篇 |
水产渔业 | 16696篇 |
畜牧兽医 | 97309篇 |
园艺 | 6304篇 |
植物保护 | 23842篇 |
出版年
2021年 | 2477篇 |
2020年 | 2858篇 |
2019年 | 3657篇 |
2018年 | 3942篇 |
2017年 | 4335篇 |
2016年 | 4773篇 |
2015年 | 4293篇 |
2014年 | 5656篇 |
2013年 | 16223篇 |
2012年 | 6270篇 |
2011年 | 8181篇 |
2010年 | 7263篇 |
2009年 | 7869篇 |
2008年 | 7558篇 |
2007年 | 6612篇 |
2006年 | 7267篇 |
2005年 | 6490篇 |
2004年 | 6328篇 |
2003年 | 6119篇 |
2002年 | 5452篇 |
2001年 | 6137篇 |
2000年 | 5734篇 |
1999年 | 5403篇 |
1998年 | 4143篇 |
1997年 | 4190篇 |
1996年 | 3916篇 |
1995年 | 4507篇 |
1994年 | 3888篇 |
1993年 | 3630篇 |
1992年 | 4347篇 |
1991年 | 4408篇 |
1990年 | 4142篇 |
1989年 | 4193篇 |
1988年 | 3658篇 |
1987年 | 3758篇 |
1986年 | 3717篇 |
1985年 | 3996篇 |
1984年 | 3670篇 |
1983年 | 3482篇 |
1982年 | 2886篇 |
1981年 | 2812篇 |
1980年 | 2768篇 |
1979年 | 3100篇 |
1978年 | 2818篇 |
1977年 | 2634篇 |
1976年 | 2463篇 |
1975年 | 2307篇 |
1974年 | 2492篇 |
1973年 | 2471篇 |
1972年 | 2205篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
971.
Cutting patterns producing high and low areas were imposed on swards of Dactylis glomerata and Lolium perenne to test whether output could be increased when compared with traditional uniform cutting methods. In two experiments, swards of both grasses were divided into parallel 9 cm strips which were cut alternately on different occasions to a height of 5 cm. These swards yielded a similar quantity of herbage DM to that from other swards cut uniformly at the same height and frequency. In a third experiment, swards of Lolium perenne were divided into alternate strips of unequal width (9 and 4.5 cm). The narrow strips were allowed to grow to a height of 15 cm and were occasionally trimmed at this height. The wide strips were cut to 5 cm at 2–or 4–weekly intervals. Areas cut to 5 cm every 2 weeks yielded significantly more DM when adjacent to high areas than when adjacent to areas cut to 5 cm every 2 weeks (i.e. under uniform cutting). The interaction between adjacent areas having different defoliation regimes is discussed in relation to the possibility of obtaining some additional output from a suitable no niform cutting system compared with uniform cutting. Sward productivity under no niform grazing patterns of livestock is also discussed. 相似文献
972.
Frank K. Pittman 《Water, air, and soil pollution》1975,4(2):215-219
The safe management of the solid radioactive waste material generated by the various operations that make up the rapidly growing nuclear electric power industry, the nuclear reactors themselves, and the plants which provide new fuel for these reactors and process the spent fuel which results from reactor operations are discussed. 相似文献
973.
974.
975.
976.
977.
Neil G. Bayfield 《Biological conservation》1974,6(4):246-251
The extent of accelerated erosion from ground damaged near ski lifts was found to have reached a peak in about 1969, with a marked decline since then. This decline was attributable to reseeding of damaged ground, provision of drains and grading of dirt roads. Burial experiments showed that where erosion debris had covered vegetation, recovery at best took several years, and with depths above about 7 cm, was almost negligible. 相似文献
978.
979.
980.
The relative-intensity X-ray fluorescence method of analysis of rock and soil samples has been investigated and compared with the net-intensity method. Strong, coherently scattered radiation originating from the X-ray tube is shown to be preferable to background radiation as an internal standard, and scattered radiation measured at one wavelength can usefully be applied in the determination of several elements. When the concentrations of an element in two soil samples of different composition (for example concretions and the soil adjacent to them) are compared, the ratio of the relative intensities may be different from the ratio of net intensities by a factor of about two. The concentrations of manganese in thirteen standard rock samples determined by the relative-intensity method are within or very close to the ranges of values reported previously. 相似文献