全文获取类型
收费全文 | 1660篇 |
免费 | 80篇 |
出版年
2023年 | 34篇 |
2022年 | 17篇 |
2021年 | 35篇 |
2020年 | 35篇 |
2019年 | 23篇 |
2018年 | 71篇 |
2017年 | 63篇 |
2016年 | 81篇 |
2015年 | 45篇 |
2014年 | 56篇 |
2013年 | 117篇 |
2012年 | 121篇 |
2011年 | 128篇 |
2010年 | 78篇 |
2009年 | 51篇 |
2008年 | 86篇 |
2007年 | 113篇 |
2006年 | 88篇 |
2005年 | 79篇 |
2004年 | 81篇 |
2003年 | 90篇 |
2002年 | 81篇 |
2001年 | 32篇 |
2000年 | 42篇 |
1999年 | 17篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1978年 | 2篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1965年 | 1篇 |
1964年 | 2篇 |
1959年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有1740条查询结果,搜索用时 15 毫秒
991.
In this work, the effects of polyamine (cadaverine, putrescine, spermidine, spermine) pretreatments on the germination of
barley seeds, seedling growth under saline (NaCI) conditions and on leaf anatomy of the seedlings grown for 20 days in pots
with perlite containing different concentrations of NaCI prepared with Hoagland solutions following the germination period
of 7 days were studied. The inhibitive effect of salt on seed germination and seedling growth was alleviated in varying degrees,
and dramatically, by polyamine pretreatments at the levels of NaCI studied; particularly with lower levels of salt, the control
seeds were able to germinate with great difficulty. Also, the successes of these pretreatments continued, even decreased,
with higher levels of NaCI such that the control seeds showed no germination. On the other hand, on the various parameters
of leaf anatomy of barley seedlings, interactions between pretreatments of polyamine and salinity, with some of these being
statistically important, were observed. 相似文献
992.
This study is related to the investigation of the Pb levels in blood of the 12 healthy University male basketball players before and after a strenuous training session by the use of square wave anodic stripping voltammetry. Although the results do not show acute lead intoxication it is obvious that blood lead levels show significant increase after training sessions. The average increase in blood lead levels is 297%. This increase is largely due to increased respiration rate during the training period. 相似文献
993.
We investigated the effects of lamotrigine, aripiprazole and escitalopram administration and experimental depression on lipid
peroxidation (LP) and antioxidant levels in cortex of the brain in rats. Forty male wistar rats were randomly divided into
five groups. First group was used as control although second group was depression-induced group. Aripiprazole, lamotrigine
and escitalopram per day were orally supplemented to chronic mild stress (CMS) depression-induced rats constituting the third,
fourth and fifth groups for 28 days, respectively. Depression resulted in significant decrease in the glutathione peroxidase
(GSH-Px) activity, reduced glutathione and vitamin C of cortex of the brain although their levels and beta-carotene concentrations
were increased by the three drugs administrations to the animals of CMS induced depression group. The LP levels in the cortex
of the brain and plasma of depression group were elevated although their levels were decreased by the administrations. The
increases of antioxidant values in lamotrigine group were higher according to aripiprazole and escitalopram supplemented groups.
Vitamin A level did not change in the five groups. In conclusion, the experimental depression is associated with elevated
oxidative stress although treatment with lamotrigine has most protective effects on the oxidative stress within three medicines. 相似文献
994.
The proopiomelanocortin-derived tridecapeptide alpha-melanocyte-stimulating hormone (alpha-MSH) is a neuropeptide that exerts broad anti-inflammatory actions in mammals. This study aimed to investigate the effect of alpha-MSH on ethanol-induced gastric ulcer in rats and to evaluate the involvement of endogenous somatostatin in the actions of the peptide. The rats received 1 mL 75% ethanol or saline orally. alpha-MSH was given (25 micro g/rat; i.p.) alone or following the somatostatin antagonist cyclo-(7-aminoheptanoyl-PH-E-d-Trp-Lys-THR) (10 microM/kg; i.p.) administration. Gastric lesions were scored macroscopically and microscopically following decapitation at 30 min after ethanol challenge. Gastric malondialdehyde (MDA) level, myeloperoxidase (MPO) activity and mast cell counts were assessed. Ethanol-induced gastric hemorrhagic lesions were characterized by increased gastric MDA level, MPO activity and mast cell counts. alpha-MSH treatment decreased the extent of tissue injury and reversed tissue MDA level, MPO activity and mast cell counts. The effect of the peptide on the severity of gastric lesions, MDA level and MPO activity was reversed by the somatostatin antagonist. In conclusion, alpha-MSH is beneficial in a rat model of gastric ulcer via mechanisms which partly involve the endogenous somatostatin. 相似文献
995.
Meryem Yeşim Çelik Mehmet Bedrettin Duman Merve Sariipek Gülşen Uzun Gören Dilara Kaya Öztürk 《Molluscan research.》2019,39(3):234-240
ABSTRACTThe fatty acid and mineral matter compositions of the visceral mass and pedal mass of wild and farmed Cornu aspersum were compared. The relative fatty acid amounts of the visceral and pedal masses of wild and farmed snails are: polyunsaturated fatty acid (PUFA) > saturated fatty acid (SFA) > monounsaturated fatty acid (MUFA), PUFA?>?SFA?>?MUFA, MUFA?>?PUFA?>?SFA and PUFA?>?MUFA?>?SFA, respectively. Wild snails had a higher concentration of iron and zinc than farmed snails. Selenium was 2.82 times higher in the pedal mass of farmed snails than the pedal mass of wild snails. Ca:P ratios in the visceral mass of wild snails, visceral mass and pedal mass of farmed snails were 1.76:1, 1.12:1 and 3.87:1 respectively. Both wild and farmed snails have high contents of oleic, linoleic, eicosapentaenoic and docosahexaenoic fatty acids and are a good source of minerals. Careful attention should be paid, however, as to which diet will be used during farming because the composition of fatty acid in the snail is affected by diet. 相似文献
996.
Nevin Çankaya İbrahim Bulduk Ayşen Melda Çolak 《Saudi Journal of Biological Sciences》2019,26(2):345-351
Colchicum autumnale L. also known as the autumn crocus, contains colchicine alkaloid having antifungal properties. The tuber of this plant is rich in terms of colchicine. In this research an ultrasound-assisted extraction (UAE) method was optimized for the extraction of colchicine from Colchicum autumnale L. bulbs before high-performance liquid chromatography with UV detection (HPLC-UV). Optimization of various extraction parameters was performed using response surface methodology (RSM) to evaluate the maximum colchicine yield from Colchicum autumnale L. bulbs. The Box-Behnken design (BBD) and RSM were used to investigate the effect of three key parameters (extraction time (20–60?min), extraction temperature (40–80?°C) and ultrasound power (500–700?W) on extraction efficiency. The variance analysis suggested that the dependent response variable of yield of colchicine may be expressed by a quadratic polynomial model. The optimal theoretical extraction conditions were found to be an ultrasonication power of 602.4?W, an extraction time of 42?min and a temperature of 64?°C. Under these conditions, the optimum foreseen yield was 0.237%. The experimental colchicine yield obtained by following the optimized conditions was found to be 0.238%. These values are very well compatible with each other. 相似文献
997.
Implications for catch composition and revenue in changing from diamond to square mesh codends in the northeastern Mediterranean
下载免费PDF全文
![点击此处可从《Zeitschrift fur angewandte Ichthyologie》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The objective of this study was to estimate the potential short‐term economic loss as a result of replacing the commercial diamond codend with a square mesh codend, and to compare fish lengths captured in 40 mm square (S40) vs 44 mm commercial hand‐woven diamond (CD44) mesh codends for red mullet (Mullus barbatus), common pandora (Pagellus erythrinus), bogue (Boops boops), European hake (Merluccius merluccius), axillary seabream (Pagellus acarne), and brushtooth lizardfish (Saurida undosquamis). A total of 20 hauls (10 hauls for S40 and 10 hauls for CD44) were conducted onboard a commercial trawler between 27 February and 11 April 2012 in Mersin Bay in the northeastern Mediterranean. Results showed that the 40 mm square mesh codend caught significantly fewer juveniles of all aforementioned species. However, when changing from the commercial diamond codend to the 40 mm square mesh codend the potential economic loss of revenue was found to be 40% in the study period, which covered the final 6 weeks of the fishing season. 相似文献
998.
Using otolith shape and morphometry to identify four Alburnus species (A. chalcoides,A. escherichii,A. mossulensis and A. tarichi) in Turkish inland waters
下载免费PDF全文
![点击此处可从《Zeitschrift fur angewandte Ichthyologie》网站下载免费的PDF全文](/ch/ext_images/free.gif)
D. Bostanci N. Polat G. Kurucu S. Yedier S. Kontaş M. Darçin 《Zeitschrift fur angewandte Ichthyologie》2015,31(6):1013-1022
Asteriscus otolith shapes as well as their morphometry and shape contours were investigated in order to identify four allopatric Alburnus species: A. chalcoides (Güldenstädt, 1772) (Ordu), A. escherichii Steindachner, 1897 (Eski?ehir), A. mossulensis Heckel, 1843 (Tunceli), and A. tarichi (Güldenstädt, 1814) (Van) in Turkish inland waters. These were compared using the shape indices (form factor, roundness, circularity, ellipticity, rectangularity and aspect ratio), and the morphological characters [otolith weight (OWE), otolith length (OL), otolith width (OW), otolith perimeter (OP), and otolith area (OA)]. The overall canonical discriminant analysis (CDA) classification score was 93.8%, with the lowest score for A. escherichii (82.5%) and the highest for A. chalcoides (100%). The otolith shapes, morphology and shape contours of all sampled fish were a clear species differentiator, thereby demonstrating that the otolith shape is species‐specific. The current study presents for the first time comprehensive variation information on interspecific left‐right asteriscus otoliths in males and females of each Alburnus species: A. chalcoides from Ordu, A. escherichii from Eski?ehir, A. mossulensis from Tunceli and A. tarichi from Van, based on a total of 307 individuals. Scanning electron microscopy (SEM) images, shape contours and other otolith characters vary within the same genus; these differences should be investigated not only in other freshwater fish species or genera but also in the same species living in different habitats. In addition, further investigation is required not only with respect to the morphometry, biometry, shape, geometry, and shape contours of the otoliths, but also regarding the genetic methods for robust identification of various sympatric and allopatric fish populations. 相似文献
999.
The endostructural pattern of a middle pleistocene human femoral diaphysis from the Karain E site (Southern Anatolia,Turkey)
下载免费PDF全文
![点击此处可从《American journal of physical anthropology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
1000.