首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1158篇
  免费   66篇
  国内免费   1篇
  2024年   3篇
  2023年   13篇
  2022年   36篇
  2021年   59篇
  2020年   31篇
  2019年   42篇
  2018年   49篇
  2017年   30篇
  2016年   42篇
  2015年   62篇
  2014年   61篇
  2013年   98篇
  2012年   89篇
  2011年   96篇
  2010年   53篇
  2009年   39篇
  2008年   43篇
  2007年   52篇
  2006年   50篇
  2005年   48篇
  2004年   53篇
  2003年   38篇
  2002年   38篇
  2001年   9篇
  2000年   3篇
  1999年   5篇
  1998年   8篇
  1996年   2篇
  1995年   3篇
  1994年   5篇
  1993年   5篇
  1991年   2篇
  1989年   2篇
  1987年   3篇
  1986年   5篇
  1985年   4篇
  1983年   3篇
  1982年   2篇
  1981年   3篇
  1980年   2篇
  1979年   3篇
  1978年   3篇
  1976年   3篇
  1975年   3篇
  1974年   3篇
  1973年   2篇
  1972年   2篇
  1968年   3篇
  1928年   2篇
  1911年   1篇
排序方式: 共有1225条查询结果,搜索用时 31 毫秒
991.
992.
993.
994.
995.
The psychoendocrinology of the development of normal gender identity and its variations is poorly understood. Studies of gender development in individuals born with endocrinologically well-characterized intersex conditions are heuristically valuable for the disaggregation of factors that are acting in concert during normal development. Four 46,XX individuals with classical congenital adrenal hyperplasia (CAH) and atypical gender identity entered a comprehensive research protocol including systematic interviews and self-report inventories on gender role behavior and identity, sexual history, and psychiatric history. Some of the data on gender variables were compared to data from 12 CAH women with the salt-wasting variant (CAH-SW) with female gender identity. The four patients (ages 28, 35, 38, and 30 years) represented three different subtypes of classical early-onset CAH: 21-OH deficiency, simple virilizing (CAH-SV); 21-OH deficiency, salt-wasting (CAH-SW); and 11-β-OH deficiency. Their medical histories were characterized by delay beyond infancy or lack of surgical feminization of the external genitalia and progressive virilization with inconsistent or absent glucocorticoid replacement therapy. Although three patients had undergone one or more genital surgeries, all had retained at least some orgasmic capacity. In regard to childhood gender-role behavior, the four gender-change patients tended to be more masculine or less feminine than (behaviorally masculinized) CAH-SW controls. All patients were sexually attracted to females only. The process of gender change was gradual and extended well into adulthood. The most plausible factors contributing to cross-gender identity development in these patients to be neither a particular genotype or endocrinotype nor a sex-typing bias on the part of the parents but a combination of a genderatypical behavioral self-image, a gender-atypical body image, and the development of erotic attraction to women. Implications for psychosocial management are also discussed.  相似文献   
996.
The effects of magnesium (Mg) supplementation on the growth performance, oxidative damage, DNA damage, and photosynthetic pigment synthesis, as well as on the activity level of carbonic anhydrase (CA), ribulose-1,5-bisphosphate carboxylase (Rubisco), and antioxidant enzymes were studied in Vicia faba L. plants exposed to heat stress (HS) and non-heat-stress (non-HS) conditions. Seeds were grown in pots containing a 1:1 mixture of sand and peat, with Mg treatments. The treatments consisted of (i) 0 Mg and non-HS (ambient temperature; control); (ii) 50 mM Mg; (iii) HS (38 °C); and (iv) 50 mM Mg and HS (38 °C). HS was imposed by placing potted plants in an incubator at 38 °C for 48 h. Growth attributes, total chlorophyll (Total Chl), and CA, and Rubisco activity decreased in plants subjected to HS, whereas accumulation of organic solutes [proline (Pro) and glycine betaine (GB)]; superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity; DNA damage; electrolyte leakage (EL); and malondialdehyde (MDA) and hydrogen peroxide (H2O2) content all increased. Application of Mg, however, significantly enhanced further proline (Pro), glycinebetaine (GB), SOD, POD, and CAT activity, and decreased DNA damage, EL, and MDA and H2O2 concentrations. These results suggest that adequate supply of Mg is not only essential for plant growth and development, but also improves plant tolerance to HS by suppressing cellular damage induced by reactive oxygen species through the enhancement of the accumulation of Pro and GB, and the actions of antioxidant enzymes.  相似文献   
997.
Agarwood (Oudh), is often used by people in the Kingdom of Saudi Arabia. The Oudh has been mentioned in the Hadith and is traditionally used for its aroma (perfuming smell) and potential medicinal applications. The aim of the study was to isolate mycotoxigenic fungi that grow on agarwood and the factors and storage conditions that enhance their growth potential. In addition to the detection of associated mycotoxins like: Aflatoxin B1 (AFB1) and ochratoxin A (OTA) from agarwood. Agarwood samples were collected from local markets of Jeddah governorate, Kingdom of Saudi Arabia. Standard dilution plate method was used for the isolation of fungi. Isolated fungi were identified based on morphological characteristics and confirmed using molecular biology techniques. AFB1 and OTA were detected by High Performance Liquid Chromatography (HLPC). The results indicated that the most commonly isolated fungal genera were in the following descending order: Aspergillus, Penicillium, Fusarium and Rhizopus. Among Aspergillus genera, A. flavus and A. ochraceus were detected based on their morphology and confirmed by PCR using specific primers. It was also noted that AFB1 was released by 15.3 and 55.0% of A. flavus and A. parasiticus isolates respectively with levels reaching up to 14.60 µg/L. The moisture content in the samples ranged from 3% to 10% affected fungal growth. AFB1 was detected in 22 out of 50 of the samples. The maximum level of AFB1 (50.7 µg/kg) was detected in samples with higher moisture content (12%) stored at a temperature of 32 °C. Aspergillus fungi were found to be the most predominant fungal genera found on agarwood. Moisture content (9–10%) and storage temperature (32 °C) stimulated fungal growth and their ability to produce mycotoxins. For this reason, storage conditions at the marketing place should be adequate in order not to provide a conducive environment for fungal growth which is associated with the mycotoxin production. In order to prevent fungal growth and mycotoxin production, it would be recommended to store agarwood at temperatures not exceeding 25 °C and moisture content of up to a maximum of 5–6%.  相似文献   
998.

Background

Pectinase enzymes present a high priced category of microbial enzymes with many potential applications in various food and oil industries and an estimated market share of $ 41.4 billion by 2020.

Results

The production medium was first optimized using a statistical optimization approach to increase pectinase production. A maximal enzyme concentration of 76.35 U/mL (a 2.8-fold increase compared with the initial medium) was produced in a medium composed of (g/L): pectin, 32.22; (NH4)2SO4, 4.33; K2HPO4, 1.36; MgSO4.5H2O, 0.05; KCl, 0.05; and FeSO4.5H2O, 0.10. The cultivations were then carried out in a 16-L stirred tank bioreactor in both batch and fed-batch modes to improve enzyme production, which is an important step for bioprocess industrialization. Controlling the pH at 5.5 during cultivation yielded a pectinase production of 109.63 U/mL, which was about 10% higher than the uncontrolled pH culture. Furthermore, fed-batch cultivation using sucrose as a feeding substrate with a rate of 2 g/L/h increased the enzyme production up to 450 U/mL after 126 h.

Conclusions

Statistical medium optimization improved volumetric pectinase productivity by about 2.8 folds. Scaling-up the production process in 16-L semi-industrial stirred tank bioreactor under controlled pH further enhanced pectinase production by about 4-folds. Finally, bioreactor fed-batch cultivation using constant carbon source feeding increased maximal volumetric enzyme production by about 16.5-folds from the initial starting conditions.
  相似文献   
999.
Despite the large number of techniques available for the transformation of bacteria, several species are still resistant to the introduction of foreign DNA. Oenococcus oeni are among the organisms that are particularly refractory to transformation. However, conjugal experiments from Lactococcus lactis to O. oeni with a new plasmid, pGID052, were performed via mobilization with success. This plasmid, a derivative of pORI19, encompasses: (i) the oriT of pIP501, which permitted the transfer to O. oeni, (ii) the replication genes of a native Leuconostoc citreum plasmid. Frequencies of 10(-7) conjugants per recipient were found. The transfer did not affect the structure of this low-copy-number plasmid. Moreover, pGID052 seems segregationally stable and could be used in the future as an expression vector.  相似文献   
1000.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号