全文获取类型
收费全文 | 1134篇 |
免费 | 47篇 |
专业分类
1181篇 |
出版年
2022年 | 9篇 |
2021年 | 12篇 |
2020年 | 12篇 |
2019年 | 10篇 |
2018年 | 12篇 |
2017年 | 15篇 |
2016年 | 25篇 |
2015年 | 38篇 |
2014年 | 36篇 |
2013年 | 59篇 |
2012年 | 63篇 |
2011年 | 48篇 |
2010年 | 35篇 |
2009年 | 40篇 |
2008年 | 46篇 |
2007年 | 40篇 |
2006年 | 46篇 |
2005年 | 32篇 |
2004年 | 31篇 |
2003年 | 53篇 |
2002年 | 46篇 |
2001年 | 36篇 |
2000年 | 37篇 |
1999年 | 31篇 |
1998年 | 15篇 |
1997年 | 6篇 |
1996年 | 17篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 23篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 34篇 |
1987年 | 15篇 |
1986年 | 24篇 |
1985年 | 16篇 |
1984年 | 14篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1979年 | 10篇 |
1977年 | 7篇 |
1975年 | 10篇 |
1974年 | 15篇 |
1973年 | 14篇 |
1972年 | 20篇 |
1971年 | 12篇 |
1967年 | 6篇 |
排序方式: 共有1181条查询结果,搜索用时 15 毫秒
1.
2.
Hitoshi Sawada Hideyoshi Yokosawa Shin-Ichi Ishii Motonori Hoshi 《Molecular reproduction and development》1982,5(3):291-301
The presence of a protease has been demonstrated in sperm of the solitary ascidian, Halocynthia roretzi, by using t-butyloxycarbonyl-L-Val-L-Pro-L-Arg-4-methylcoumaryl-7-amide (Boc-Val-Pro-Arg-MCA) and other arginyl or lysyl MCA derivatives as substrates. Several properties of the enzyme were investigated in a crude extract. The activity had a pH optimum near 8.0 and was enhanced by the addition of CaCl2. The Km value of 87μM was determined for Boc-Val-Pro-Arg-MCA under the optimal conditions. An apparent molecular weight was estimated to be 35,000 by gel filtration. The enzyme was inhibited with diisopropyl fluorophosphate, leupeptin, antipain, p-aminobenzamidine, Val-Pro-Arg-CH2Cl, and soybean trypsin inhibitor, but scarcely inhibited with chymostatin, elastatinal, p-chloromercuribenzoic acid, tosyl-Lys-CH2Cl, and tosyl-Phe-CH2Cl. Boc-Val-Pro-Arg-MCA, the most susceptible of the substrates examined, showed the most effective inhibition against fertilization of ascidian eggs. Thus, this enzyme in ascidian sperm extract has features closely similar to mammalian acrosin [EC 3.4.21.10], and we conclude that the enzyme is involved in fertilization as one of the lysins. 相似文献
3.
Resting spore formation during short time-scale upwelling and its significance were investigated in the field and by a simple
theoretical model. Field observations of spore formation ofLeptocylindrus danicus were made off Izu Peninsula, Japan. A rapid increase in ratio of resting spore to vegetative cell numbers indicated thatL. danicus formed resting spores quickly as a response to nutrient depletion in the upwelled water, although only a very low number
of resting spores was found in the upwelling. A simple model was constructed to investigate the possible advantages of spore
formation during short time-scale upwelling. This showed that there is a critical time-scale for resting spore formation to
be advantageous. The nutrient depletion period of the upwelling off Izu was shorter than the critical time-scale determined
by the model. Rapid-sinking of resting spores may increase further the critical time-scale, unless spores return with upwelling
water. For short time-scale upwelling, the vegetative cell may be better suited than the resting spore for enduring a short
period of nutrient depletion.
Contribution from Shimoda Marine Research Center, University of Tsukuba, No. 475. 相似文献
4.
CAM Photosynthesis under Drought Conditions in Kalanchoe blossfeldiana Grown with Nitrate or Ammonium as the Sole Nitrogen Source 总被引:1,自引:0,他引:1
K. blossfeldiana Poelln. cv. Hikan was grown in vermiculite,supplied daily with nutrient solution containing 1 mM (or 10mM) nitrate or ammonium as the sole nitrogen source. The nitrate-grownplants had more activity of CAM (Crassulacean acid metabolism)photosynthesis (nocturnal CO2 uptake in the shoot and nocturnalincreases of titratable acidity and malate content in the leaves)than the ammonium-grown plants. Interruption of the solutionsupply for 5 or more days (drought conditions) increased theactivity of CAM photosynthesis in nitrate- or ammonium-grownplants, and the diurnal CO2 uptake pattern in the nitrate-grownplants shifted from weak-CAM to full-CAM.The difference in the activity of CAM photosynthesis betweennitrate- and ammonium-grown plants increased under the droughtconditions. When the solution was resupplied, the activity ofCAM photosynthesis rapidly decreased to the levels before theinterruption. The physiological mechanism and ecological significanceof the effect of the nitrogen source on CAM photosynthesis arediscussed (Received January 5, 1988; Accepted April 13, 1988) 相似文献
5.
Kazuo Ota Soji Kurita Kazumasa Yamada Tohru Masaoka Yoshiro Uzuka Nobuya Ogawa 《Cancer immunology, immunotherapy : CII》1986,23(1):5-10
Summary In a cooperative randomized control study of immunotherapy with bestatin in combination with chemotherapy in adults with acute nonlymphocytic leukemia (ANLL), 101 patients (48 in the bestatin group and 53 in the control group) out of 115 patients registered were evaluated as eligible. The bestatin group achieved a statistically significant prolongation of survival compared with the control group in overall ANLL and acute myelogenous leukemia. In the analysis of patient age, the bestatin group achieved a statistically significant prolongation of both the remission duration and survival in patients aged 50 to 65 years, while the differences were not significant in the 15 to 49 age group. The bestatin group tended to achieve a higher rate of reinduction of remission in patients who had recurrence of leukemia. Side effects developed in only 5 (9.6%) of 52 patients treated with bestatin. None of these side effects were particularly serious in nature. It is concluded that bestatin is useful for prolongation of survival of adult patients with ANLL, making for a longer remission duration especially in elderly patients and with few side effects. 相似文献
6.
A number of epoxides, including cis- and trans-stilbene oxides, were assayed as substrates for epoxide hydrolases (EHs) by gas-liquid chromatography. Radiolabeled stilbene oxides were prepared by sodium borotritide reduction of desyl chloride followed by ring closure with base treatment. Rapid radiometric assays for EHs were performed by differential partitioning of the epoxide into dodecane, while the product diol remained in the aqueous phase. Glutathione (GSH) transferase was similarly assayed by partitioning the epoxide and diol, if formed metabolically, into 1-hexanol, while the GSH conjugate was retained in the aqueous phase. The cytosolic EH rapidly hydrates the trans isomer while the cis is very poorly hydrated. In contrast, the cis is a better substrate for the microsomal EH than the trans. GSH transferase utilized both epoxides as substrates, but conjugation is faster with the cis isomer. Cytosolic EH activity is high in mouse but very low in rat and guinea pig. Microsomal EH activity, in contrast, is highest in guinea pig, intermediate in rat, and the lowest in mouse. GSH transferase activity, which is high in all three species, can be inhibited by chalcone, with an I50 of 3.1 × 10?5m. These assays facilitate the rapid evaluation and direct comparison of epoxide-metabolizing systems in cell homogenates used in short-term mutagenicity assays, cell or organ culture, and possibly in vivo. 相似文献
7.
Identification of Cytokinins in Root Exudate of the Rice Plant 总被引:4,自引:0,他引:4
Murofushi Noboru; Inoue Ayumu; Watanabe Naoharu; Ota Yasuo; Takahashi Nobutaka 《Plant & cell physiology》1983,24(1):87-92
Cytokinins, cis-zeatin and cis- and (trans-ribosylzeatin, wereidentified in the root exudate of the rice plant (Oryza sativa,indica cultivar IR-24) after several chromatographic separationsand combined gas-liquid chromatography-selected ion monitoring(GC-SIM) analysis. The presence of trans-zeatin ribotide wassuggested by enzyme hydrolysis, subsequent chromatographic separationand GC-SIM. The comparatively high content of the ribotide inthe root exudate suggests the form of cytokinins to be transportedfrom roots to other parts in the rice plant. (Received July 22, 1982; Accepted November 25, 1982) 相似文献
8.
9.
10.