全文获取类型
收费全文 | 767篇 |
免费 | 47篇 |
国内免费 | 55篇 |
出版年
2024年 | 2篇 |
2023年 | 12篇 |
2022年 | 15篇 |
2021年 | 24篇 |
2020年 | 21篇 |
2019年 | 30篇 |
2018年 | 14篇 |
2017年 | 32篇 |
2016年 | 22篇 |
2015年 | 35篇 |
2014年 | 27篇 |
2013年 | 50篇 |
2012年 | 36篇 |
2011年 | 45篇 |
2010年 | 21篇 |
2009年 | 36篇 |
2008年 | 41篇 |
2007年 | 33篇 |
2006年 | 40篇 |
2005年 | 53篇 |
2004年 | 25篇 |
2003年 | 22篇 |
2002年 | 25篇 |
2001年 | 20篇 |
2000年 | 16篇 |
1999年 | 12篇 |
1998年 | 3篇 |
1997年 | 16篇 |
1996年 | 5篇 |
1995年 | 16篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 3篇 |
排序方式: 共有869条查询结果,搜索用时 15 毫秒
1.
Two new oleanane-type triterpene saponins, identified as 16α-hydroxy-22-O-angeloyl-23-formyl-28,31-dihydroxymethylene-olean-12-ene-3β-O-{β-d-galactopyranosyl-(1 → 2)[β-d-xylopyranosyl-(1 → 2)-α-l-arabinopyranosyl(1 → 3)]-β-d-glucopyranosiduronic acid} (oleiferasaponin B1, 1) and 22-O-hydrocinnamoyl-23-formyl-28-dihydroxymethylene-olean-12-ene-3β-O-{β-d-glucopyranosyl-(1 → 2)[β-d-xylopyranosyl-(1 → 2)-α-l-arabinopyranosyl(1 → 3)]-β-d-glucopyranosiduronic acid} (oleiferasaponin B2, 2), were isolated from the seed cake of Camellia oleifera Abel. Their structures were established by extensive 1D- and 2D-NMR experiments along with TOF-MS analysis and acid hydrolysis. The cytotoxicity of the isolated compounds was evaluated in four human carcinoma cell lines: A 549, SK-OV-3, SK-MEL-2 and HCT15. Both compounds 1 and 2 exhibited significantly cytotoxic activity with IC50 values of 18.5 μM (A549), 11.3 μM (SK-OV-3), 13.9 μM (SK-MEL-2) and 1.6 μM (HCT15) for 1 and IC50 values of 8.4 μM (A549), 6.3 μM (SK-OV-3), 9.2 μM (SK-MEL-2) and 0.8 μM (HCT15) for 2. In addition, compound 2 showed more effective cytotoxic activity than compound 1. 相似文献
2.
Electron probe microanalysis of transverse sections was used to provide semiquantitative estimates of Al and other cations
in the leaf tissues of some Al-accumulating plants of the cerrado vegetation of central Brazil. Concentrations of Al were
generally higher than those of other cations in the phloem elements of these plants growing on dystrophic as well as fertile
acid soils. When one of the Al-accumulating species,Vochysia thyrsoidea, was grown in a calcareous soil, the concentration of Al in the phloem elements of leaves was lower than that of Ca and K
though the cotyledons showed higher concentrations of Al than those of other cations. 相似文献
3.
Synopsis The caloric density of stomach contents in juvenile chinook salmon,Oncorhynchus tshawytscha, was not affected by gastric evacuation, suggesting a constant caloric density of stomach contents during evacuation. Differences in the caloric density of prey consumed did affect caloric density of stomach contents over a 24-h period. Consumption of the amphipodCorophium sp. was associated with reduced caloric densities of stomach contents. During periods whenCorophium contributed more than 4% of the stomach contents, average caloric density declined from 5.56 to 5.33 kcal g–1. Despite this difference, estimates of daily energy intake of juvenile chinook salmon were only 3%, greater when developed from the mean caloric density of stomach contents excludingCorophium. 相似文献
4.
Summary As a part of integrated study of makhana, the mineral contents of the plant parts and the fruits of makhana (Euryale ferox) have been presented here. It has been observed that the fruits were not only rich in minerals but also in protein. The plant
parts also contained high amounts of micronutrients. Its fruits are, therefore, a good supplement for minerals which are produced
from otherwise agriculturally waste (water-logged) areas. 相似文献
5.
Mitsuhiko Sano 《Environmental Biology of Fishes》1989,25(1-3):195-203
Synopsis Stomach content data from 32 species of Japanese butterflyfishes of the family Chaetodontidae were used to classify them into
feeding groups and to determine their important food resources. Four major feeding groups were distinguished: (1) obligative
coral feeders which prey exclusively or mostly on Scleractinian corals, (2) facultative coral feeders that take both corals
and other benthic organisms, (3) noncoralline invertebrate feeders which consume benthic invertebrates other than corals,
and (4) zooplankton feeders. Ten species representing 31% of the butterflyfishes belong to the first category. The second
and third categories include 13 (41%) and 8 (25%) species, respectively. The fourth category is represented by only one species
which picks individual zooplankters, especially calanoid copepods, in midwater above the reefs. Facultative coral feeders
consumed varying quantities of scleractinians (from 2 to 74% of food volume), along with a variety of benthic organisms including
algae, alcyonarians, sea anemones, sedentary polychaetes, sponges, hydroids, etc. Noncoralline invertebrate feeders, on the
other hand, tend to have low diversified diets, predominated by one prey item such as sea anemones, zoanthideans, polychaetes,
or colonial ascidians. These dietary data suggest that scleractinian corals are the most important food resource for the Japanese
butterflyfishes, and next important are sea anemones, sedentary polychaetes, alcyonarians, and algae. 相似文献
6.
Renée M. Borges 《Oecologia》1990,85(1):80-86
Summary The calcium ingestion of Malabar Giant Squirrels Ratufa indica (Sciuridae) was examined at two sites, Magod and Bhimashankar, in western India. In females at Magod a positive correlation was found between rates of calcium ingestion from food resources and the contribution of those resources to the daily diet. This relationship was true for all females at Magod irre-spective of their reproductive condition. This relationship was neither significant for males at the same site nor for both sexes at Bhimashankar. A differential requirement for calcium between the sexes and the occurrence of higher rates of calcium ingestion or the probable presence of more easily digestible calcium at Bhimashankar are postulated to explain the observed phenomenon. Mature leaves and bark appear to be reliable sources of calcium at these sites. 相似文献
7.
A. Le Ralec 《BioControl》1995,40(1):87-93
Using transmission electron microscopy, egg content is studied in 10 parasitoid species, which either feed on host hemolymph or do not. As expected, hydropic eggs were found to contain little yolk which is only lipoid. In host-feeding species, the yolk contains a great number of typical protein bodies whereas in species that do not host-feed and which produce large eggs, the yolk contain very different bodies. 相似文献
8.
9.
Aristóteles Philippe Nunes Queiroz Maria Lúcia Góes Araújo Nigel E. Hussey Rosângela P. T. Lessa 《Journal of fish biology》2023,102(1):27-43
Understanding the ecological role of species with overlapping distributions is central to inform ecosystem management. Here we describe the diet, trophic level and habitat use of three sympatric stingrays, Hypanus guttatus, H. marianae and H. berthalutzae, through combined stomach content and stable isotope (δ13C and δ15N) analyses. Our integrated approach revealed that H. guttatus is a mesopredator that feeds on a diverse diet of benthic and epibenthic marine and estuarine organisms, principally bivalve molluscs, Alpheus shrimp and teleost fishes. Isotopic data supported movement of this species between marine and estuarine environments. H. berthalutzae is also a marine generalist feeder, but feeds primarily on teleost fishes and cephalopods, and consequently occupies a higher trophic level. In contrast, H. marianae is a mesopredator specialized on shrimps and polychaetas occurring only in the marine environment and occupying a low niche breadth. While niche overlap occurred, the three stingrays utilized the same prey resources at different rates and occupied distinct trophic niches, potentially limiting competition for resources and promoting coexistence. These combined data demonstrate that these three mesopredators perform different ecological roles in the ecosystems they occupy, limiting functional redundancy. 相似文献
10.
摘要 目的:探讨三七总皂苷联合顺铂对胃癌大鼠肾损伤的改善作用并分析潜在机制。方法:选择60只健康SD雄性大鼠分为对照组、胃癌模型组、顺铂组及三七总皂苷组,各15只。除对照组外,其余组大鼠采用皮下接种胃癌BGC823细胞悬液法建立胃癌模型。建模成功后,给予对照组和胃癌模型组大鼠生理盐水腹腔注射和灌胃,给予顺铂组大鼠腹腔注射25 mg/kg顺铂注射液并灌胃生理盐水,给予三七总皂苷组大鼠腹腔注射25 mg/kg顺铂注射液并灌胃30 mg/kg三七总皂苷。分别于建模成功时、药物处理28 d时采用酶联免疫吸附法检测血清肌酐(SCr)、尿素氮(BUN)和尿液β-N-乙酰氨基葡萄糖苷酶(NAG)、肾损伤分子1(KIM-1)水平。处死大鼠后取肾脏,分别测定肾脏组织匀浆中超氧化物歧化酶(SOD)、丙二醛(MDA)、过氧化氢酶(CAT)、谷胱甘肽(GSH)水平,制备肾脏组织石蜡切片并行苏木精-伊红染色后观察大鼠肾组织的病理学变化。采用TUNEL染色法检测肾脏组织细胞凋亡情况,采用Western Blotting法检测肾脏组织中LC3、HIF-1α和Beclin1 蛋白表达情况。结果:顺铂组和三七总皂苷组大鼠血清SCr、BUN和尿液NAG、KIM-1水平均显著高于对照组和模型组(P<0.05),三七总皂苷组大鼠血清SCr、BUN和尿液NAG、KIM-1水平显著高于顺铂组(P<0.05)。三七总皂苷组大鼠肾脏组织SOD、GSH水平显著低于模型组但显著高于顺铂组,MDA显著高于模型组但显著低于顺铂组(P<0.05),CAT与模型组无显著差异(P<0.05),但显著高于顺铂组(P>0.05)。顺铂组大鼠肾小管明显扩张、管腔狭窄,基底层上皮细胞水肿、坏死并形成空泡,肾小管。三七总皂苷组大鼠肾脏病理学改变程度显著轻于顺铂组。顺铂组和三七总皂苷组大鼠肾脏组织细胞凋亡指数显著增加,三七总皂苷组大鼠肾脏组织细胞凋亡指数显著低于顺铂组(P<0.05)。顺铂组大鼠肾脏组织中LC3、HIF-1α和Beclin1蛋白水平均显著高于模型组,但显著低于三七总皂苷组(P<0.05)。结论:三七总皂苷可能通过减轻过氧自由基和过氧化水平、增强线粒体自噬水平减少肾组织细胞凋亡,减轻顺铂引起的胃癌大鼠肾损伤。 相似文献