全文获取类型
收费全文 | 6195篇 |
免费 | 394篇 |
国内免费 | 451篇 |
专业分类
7040篇 |
出版年
2024年 | 12篇 |
2023年 | 113篇 |
2022年 | 101篇 |
2021年 | 160篇 |
2020年 | 189篇 |
2019年 | 232篇 |
2018年 | 168篇 |
2017年 | 178篇 |
2016年 | 199篇 |
2015年 | 246篇 |
2014年 | 260篇 |
2013年 | 367篇 |
2012年 | 211篇 |
2011年 | 250篇 |
2010年 | 203篇 |
2009年 | 325篇 |
2008年 | 356篇 |
2007年 | 346篇 |
2006年 | 330篇 |
2005年 | 268篇 |
2004年 | 246篇 |
2003年 | 268篇 |
2002年 | 183篇 |
2001年 | 158篇 |
2000年 | 161篇 |
1999年 | 120篇 |
1998年 | 134篇 |
1997年 | 137篇 |
1996年 | 98篇 |
1995年 | 88篇 |
1994年 | 97篇 |
1993年 | 93篇 |
1992年 | 106篇 |
1991年 | 71篇 |
1990年 | 71篇 |
1989年 | 60篇 |
1988年 | 54篇 |
1987年 | 45篇 |
1986年 | 53篇 |
1985年 | 64篇 |
1984年 | 31篇 |
1983年 | 24篇 |
1982年 | 29篇 |
1981年 | 33篇 |
1980年 | 18篇 |
1979年 | 15篇 |
1978年 | 13篇 |
1974年 | 17篇 |
1973年 | 13篇 |
1972年 | 8篇 |
排序方式: 共有7040条查询结果,搜索用时 218 毫秒
991.
992.
993.
Salinity and submergence are two very prominent abiotic stress conditions affecting rice yield adversely in the coastal agro ecosystem. Marker Assisted Backcross Breeding (MABB) is an efficient and fast track molecular tool to incorporate a desired stress tolerant QTL/gene into an improved cultivar. The present study was carried out for the introgression of Saltol QTL responsible for salinity tolerance and Sub1 gene responsible for submergence tolerance into the high yielding rice variety Aiswarya independently through MABB. Final objective of the study is to develop dual stress tolerant (tolerance to salinity and submergence) Aiswarya rice variety by pyramiding the both target QTLs introgressed BC2F2 progenies having maximum background homozygosity. The donors of Saltol QTL and Sub1 gene used in the present study were FL478 and Swarna Sub1, respectively. Based on the background genome analysis of the introgressed plants, the plants with > 85–90% background similarity were selected for pyramiding of Saltol QTL and Sub1 gene into the elite background of rice variety Aiswarya. Those selected introgressed lines with Saltol QTL and Sub1 gene will be again crossed to pyramid both Saltol QTL and Sub1 gene into the rice variety Aiswarya. Such a mega rice variety pyramided with dual stress tolerant QTLs is the expected outcome of this study and can be recommended for cultivation in the flood prone saline coastal agroecosystem. 相似文献
994.
995.
《Saudi Journal of Biological Sciences》2023,30(2):103537
Water scarcity is of growing concern in many countries around the world, especially within the arid and semi-arid zones. Accordingly, rationalizing irrigation water has become an obligation to achieve the sustainable developmental goals of these countries. This may take place via using deficit irrigation which is long thought to be an effective strategy to save and improve water productivity. The current study is a trial to evaluate the pros and cons of using 50 and 75 % of the irrigation requirements (IR) of wheat (deficit irrigations) versus 100 %IR, while precisely charting changes in wheat growth parameters, antioxidant enzymes in plant shoots and the overall nutritional status of plants (NPK contents). Accordingly, a field experiment was conducted for two successive seasons, followed a split-plot design in which deficit irrigations (two irrigations to achieve 50 % of the irrigations requirements (IR), three irrigations to attain 75 % IR, and four irrigations to fulfill 100 % IR) were placed in main plots while four different studied wheat cultivars were in subplots. Results obtained herein indicate that deficit irrigations led to significant reductions in growth parameters and productivity of all wheat cultivars, especially when using 50 % IR. It also decreased NPK contents within plant shoots while elevated their contents of proline, peroxidase, and catalase enzymes. On the other hand, this type of irrigation decreased virtual water content (VWC, the amount of water used in production on ton of wheat grains). Stress tolerance index (STI), and financial revenues per unit area were also assessed. The obtained values of grain productivity, STI, VWC and financial revenues were weighted via PCA analyses, and then introduced in a novel model to estimate the efficiency of deficit irrigations (ODEI) whose results specified that the overall efficiency decreased as follows: 50 %IR < 75 %IR < 100 %IR. In conclusion, deficit irrigation is not deemed appropriate for rationalizing irrigation water while growing wheat on arid soils. 相似文献
996.
Catherine Kiwuka Jan Vos Jacob C. Douma Pascal Musoli John W. Mulumba Valérie Poncet Niels P. R. Anten 《Ecology and evolution》2023,13(1):e9715
Uganda lies within the drier end of the natural distribution range of Coffea canephora and contains unexplored genetic material that could be drought-adapted and useful for developing climate-resilient varieties. Using water treatment: (i) ample and (ii) restricted-water, the response of 148 genotypes were studied comprising wild, feral and cultivated C. canephora. Biomass allocation, standing leaf area and leaf area growth data were collected. Linear mixed effect models and PCA were used to the analyze effect of water treatment on genotypes from different: (i) cultivation status, (ii) genetic groups and (iii) locations. We also assessed the relationship between drought tolerance for relative growth rate in leaf area (RGRA), total number of leaves (TNL), total leaf area (TLA) and total leaf dry weight (TLDW) of genotypes at final harvest. Restricted-water reduced RGRA across genetic groups (3.2–32.5%) and locations (7.1–36.7%) but not cultivation status. For TNL, TLA and TLDW, genotypes that performed well in ample-water performed worse under restricted-water, indicating growth-tolerance trade-off. Drought tolerance in RGRA and TNL were negatively correlated with wetness index suggesting some degree of adaptation to local climate. Findings indicate a growth-tolerance trade-off within this tropical tree species and drought tolerance of Uganda's C. canephora is somewhat associated with local climate. 相似文献
997.
Two alkaline saline inland lakes of Indian arid region were studied during 1984 and 1985, to assess functioning and interaction of various environmental and biological factors. Changes in physical and chemical variables, planktonic composition, chlorophyll content and phytoplankton primary productivity were examined.Salinity in both lakes fluctuated from almost fresh water (1.80), to hypersaline (300) and acted as the main controlling factor for almost all the biotic parameters. Maximum total alkalinities were 2162 mg l–1 and 2090 mg l–1, respectively in Sambhar and Didwana lakes. Dissolved oxygen ranged from completely anoxic conditions to maxima of 11.68 and 7.29 mg 1–1, respectively in Sambhar and Didwana lakes. Nutrient enrichment in the lakes was low.The phytoplankton species composition of Sambhar lake was reduced from an earlier reported 20 genera to only 11 (Nostoc, Microcystis, Spirulina, Aphanocapsa, Oscillatoria, Merismopedia, Nitzschia, Navicula, Synedra, Cosmarium and Closterium). Phytoplankton of Didwana was composed of only 9 genera including Anabaena and Nodularia. Sambhar lake, which once contained Artemia, is now totally devoid of them. On the other hand, Artemia was the most dominant zooplankter in Didwana lake at a salinity range of 15–288. Other zooplankters such as Moina, Cyclops and Brachionus flourished at lower salinity levels in Didwana lake. The seasonal quantitative and qualitative phyto- and zooplankton changes in relation to salinity are documented. 相似文献
998.
999.
《DNA Repair》2017
Inappropriate repair of UV-induced DNA damage results in human diseases such as Xeroderma pigmentosum (XP), which is associated with an extremely high risk of skin cancer. A variant form of XP is caused by the absence of Polη, which is normally able to bypass UV-induced DNA lesions in an error-free manner. However, Polη is highly error prone when replicating undamaged DNA and, thus, the regulation of the proper targeting of Polη is crucial for the prevention of mutagenesis and UV-induced cancer formation. Spartan is a novel regulator of the damage tolerance pathway, and its association with Ub-PCNA has a role in Polη targeting; however, our knowledge about its function is only rudimentary. Here, we describe a new biochemical property of purified human SPARTAN by showing that it is a DNA-binding protein. Using a DNA binding mutant, we provide in vivo evidence that DNA binding by SPARTAN regulates the targeting of Polη to damage sites after UV exposure, and this function contributes highly to its DNA-damage tolerance function. 相似文献
1000.