全文获取类型
收费全文 | 2003篇 |
免费 | 123篇 |
国内免费 | 9篇 |
专业分类
林业 | 151篇 |
农学 | 118篇 |
基础科学 | 38篇 |
461篇 | |
综合类 | 145篇 |
农作物 | 268篇 |
水产渔业 | 188篇 |
畜牧兽医 | 440篇 |
园艺 | 75篇 |
植物保护 | 251篇 |
出版年
2024年 | 3篇 |
2023年 | 19篇 |
2022年 | 57篇 |
2021年 | 78篇 |
2020年 | 95篇 |
2019年 | 125篇 |
2018年 | 142篇 |
2017年 | 130篇 |
2016年 | 133篇 |
2015年 | 71篇 |
2014年 | 85篇 |
2013年 | 213篇 |
2012年 | 111篇 |
2011年 | 131篇 |
2010年 | 105篇 |
2009年 | 68篇 |
2008年 | 121篇 |
2007年 | 57篇 |
2006年 | 45篇 |
2005年 | 38篇 |
2004年 | 33篇 |
2003年 | 32篇 |
2002年 | 24篇 |
2001年 | 17篇 |
2000年 | 27篇 |
1999年 | 16篇 |
1998年 | 15篇 |
1997年 | 12篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1979年 | 5篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有2135条查询结果,搜索用时 31 毫秒
991.
Signal transduction and the control of gene expression 总被引:1,自引:0,他引:1
992.
Plaut JJ Picardi G Safaeinili A Ivanov AB Milkovich SM Cicchetti A Kofman W Mouginot J Farrell WM Phillips RJ Clifford SM Frigeri A Orosei R Federico C Williams IP Gurnett DA Nielsen E Hagfors T Heggy E Stofan ER Plettemeier D Watters TR Leuschen CJ Edenhofer P 《Science (New York, N.Y.)》2007,316(5821):92-95
The ice-rich south polar layered deposits of Mars were probed with the Mars Advanced Radar for Subsurface and Ionospheric Sounding on the Mars Express orbiter. The radar signals penetrate deep into the deposits (more than 3.7 kilometers). For most of the area, a reflection is detected at a time delay that is consistent with an interface between the deposits and the substrate. The reflected power from this interface indicates minimal attenuation of the signal, suggesting a composition of nearly pure water ice. Maps were generated of the topography of the basal interface and the thickness of the layered deposits. A set of buried depressions is seen within 300 kilometers of the pole. The thickness map shows an asymmetric distribution of the deposits and regions of anomalous thickness. The total volume is estimated to be 1.6 x 10(6) cubic kilometers, which is equivalent to a global water layer approximately 11 meters thick. 相似文献
993.
Zarrin AA Del Vecchio C Tseng E Gleason M Zarin P Tian M Alt FW 《Science (New York, N.Y.)》2007,315(5810):377-381
Antibody class switching in activated B cells uses class switch recombination (CSR), which joins activation-induced cytidine deaminase (AID)-dependent double-strand breaks (DSBs) within two large immunoglobulin heavy chain (IgH) locus switch (S) regions that lie up to 200 kilobases apart. To test postulated roles of S regions and AID in CSR, we generated mutant B cells in which donor Smu and accepter Sgamma1 regions were replaced with yeast I-SceI endonuclease sites. We found that site-specific I-SceI DSBs mediate recombinational IgH locus class switching from IgM to IgG1 without S regions or AID. We propose that CSR evolved to exploit a general DNA repair process that promotes joining of widely separated DSBs within a chromosome. 相似文献
994.
Zhang M Fang S Zakhidov AA Lee SB Aliev AE Williams CD Atkinson KR Baughman RH 《Science (New York, N.Y.)》2005,309(5738):1215-1219
Individual carbon nanotubes are like minute bits of string, and many trillions of these invisible strings must be assembled to make useful macroscopic articles. We demonstrated such assembly at rates above 7 meters per minute by cooperatively rotating carbon nanotubes in vertically oriented nanotube arrays (forests) and made 5-centimeter-wide, meter-long transparent sheets. These self-supporting nanotube sheets are initially formed as a highly anisotropic electronically conducting aerogel that can be densified into strong sheets that are as thin as 50 nanometers. The measured gravimetric strength of orthogonally oriented sheet arrays exceeds that of sheets of high-strength steel. These nanotube sheets have been used in laboratory demonstrations for the microwave bonding of plastics and for making transparent, highly elastomeric electrodes; planar sources of polarized broad-band radiation; conducting appliqués; and flexible organic light-emitting diodes. 相似文献
995.
Sharakhov IV Serazin AC Grushko OG Dana A Lobo N Hillenmeyer ME Westerman R Romero-Severson J Costantini C Sagnon N Collins FH Besansky NJ 《Science (New York, N.Y.)》2002,298(5591):182-185
In tropical Africa, Anopheles funestus is one of the three most important malaria vectors. We physically mapped 157 A. funestus complementary DNAs (cDNAs) to the polytene chromosomes of this species. Sequences of the cDNAs were mapped in silico to the A. gambiae genome as part of a comparative genomic study of synteny, gene order, and sequence conservation between A. funestus and A. gambiae. These species are in the same subgenus and diverged about as recently as humans and chimpanzees. Despite nearly perfect preservation of synteny, we found substantial shuffling of gene order along corresponding chromosome arms. Since the divergence of these species, at least 70 chromosomal inversions have been fixed, the highest rate of rearrangement of any eukaryote studied to date. The high incidence of paracentric inversions and limited colinearity suggests that locating genes in one anopheline species based on gene order in another may be limited to closely related taxa. 相似文献
996.
Owais Ali WANI Shamal Shasang KUMAR Nazir HUSSAIN Anas Ibni Ali WANI Subhash BABU Parvej ALAM Megna RASHID Simona Mariana POPESCU Sheikh MANSOOR 《土壤圈》2023,33(2):250-267
Carbon(C) is a key constitutive element in living organisms(plants, microbes, animals, and humans). Carbon is also a basic component of agriculture because it plays a dynamic role in crop growth, development, nutrient cycling, soil fertility, and other agricultural features. The presence of C enhances soil physical, chemical, and biological properties. The C cycle supports all life on the Earth by transferring C between living organisms and the environment. The global climate is changing, and th... 相似文献
997.
Ali Tahir Ishtiaq Ayesha Mushtaq Iram Ayaz Neelum Jan Muhammad Ishtiaq Khan Wajiha Khan Uzma Murtaza Iram 《Plant foods for human nutrition (Dordrecht, Netherlands)》2021,76(4):501-506
Plant Foods for Human Nutrition - Diabetic kidney disease is one of the most common microvascular complications of diabetes mellitus with consequences of diabetic nephropathy. Here we amined to... 相似文献
998.
Abrar Muhammad Mohsin Xu Hu Aziz Tariq Sun Nan Mustafa Adnan Aslam Muhammad Wajahat Shah Syed Atizaz Ali Mehmood Khalid Zhou Baoku Ma Xingzhu Chen Xianni Xu Minggang 《Journal of Soils and Sediments》2021,21(2):705-723
Journal of Soils and Sediments - Soil organic carbon (SOC) is an important parameter determining soil fertility and sustaining soil health. How C, N, and P contents and their stoichiometric ratios... 相似文献
999.
Ahmet Kurunc Ali Unlukara Bilal Cemek 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(6):514-522
Abstract There is a growing realization that an increasing number of countries are approaching full utilization of their conventional water resources and that the quantity of good-quality water supplies available to agriculture is diminishing. Effects of irrigation regime and irrigation water salinity on bell pepper including yield, fruit number and quality, vegetative and root growth, evapotranspiration and water use efficiency were investigated in this study by conducting two different experiments. Six different salinity levels of irrigation water and four different irrigation regimes were used as treatments. Considering the results from irrigation water salinity experiment, it can be concluded that as soil salinity increases, water consumption, water use efficiency, yield and other vegetative growth parameters of bell pepper were decreased. A polynomial relationship between soil salinity and water consumption was observed. It was found that bell pepper is moderately sensitive to salinity with a 1.2 dS m?1 threshold and a 10.9% slope value. In the irrigation regime experiment, limited irrigation caused decreases in water consumption, yield and vegetative growth of bell pepper. Yield response factors were close in the cases of irrigation regime (1.50) and irrigation water salinity (1.40). Total soluble solids of bell pepper were increased due to both irrigation water salinity and water application rate but not dry matter ratio. Considerable water consumption decreases because of salinity were determined. Therefore, the effect of irrigation water salinity should be considered in irrigation management to prevent excess saline water application and to protect the environment. 相似文献
1000.
The genetic diversity of the genus Lathyrus is of significant importance, particularly for its role in sustaining the livelihoods of local communities living under very harsh conditions and its potential to adapt to climate change. Grasspea (L. sativus) is the most widely used species and to a lesser extent L. cicera and L. ochrus, each is used for animal feed in many parts of the world and food in poorer regions, but human over-consumption of the seeds can lead to lathyrism, a disease caused by neurotoxins. This study has added substantial information and accuracy to the existing global Lathyrus database by combining diverse datasets and by adding information of major herbaria from Europe. This global Lathyrus database, available at ICARDA, was used to conduct gap analysis to guide future collecting missions and in situ conservation efforts for highest priority species originating from the Mediterranean Basin, and Caucasus, Central and West Asia region. The results showed the highest concentration of Lathyrus priority species are found in the Fertile Crescent countries, France, Italy and Greece. The area either side of the Lebanese/Syrian border near Tel Kalakh, Syria was identified as the hotspot and the overall priority location for establishing the first in situ genetic reserve. The gap analysis for ex situ conservation shows that only six species (representing 16.6 %) of the 36 priority species are adequately sampled. Only L. cicera has already been well sampled among the closely related species to cultivated species L. sativus, indicating further collecting of L. amphicarpos, L. belinensis, L. chrysanthus, L. hirticarpus, L. hirsutus and L. marmoratus is required. In addition, six secondary priority Lathyrus species have no ex situ collections (L. lentiformis, L. lycicus, L. phaselitanus, L. trachycarpus, L. tremolsianus and L. undulatus) and also require targeted collecting. 相似文献