全文获取类型
收费全文 | 697篇 |
免费 | 78篇 |
出版年
2021年 | 8篇 |
2020年 | 6篇 |
2018年 | 11篇 |
2017年 | 7篇 |
2016年 | 11篇 |
2015年 | 25篇 |
2014年 | 32篇 |
2013年 | 30篇 |
2012年 | 21篇 |
2011年 | 34篇 |
2010年 | 10篇 |
2009年 | 16篇 |
2008年 | 28篇 |
2007年 | 31篇 |
2006年 | 29篇 |
2005年 | 29篇 |
2004年 | 30篇 |
2003年 | 18篇 |
2002年 | 18篇 |
2001年 | 30篇 |
2000年 | 29篇 |
1999年 | 22篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 26篇 |
1991年 | 19篇 |
1990年 | 20篇 |
1989年 | 14篇 |
1988年 | 22篇 |
1987年 | 13篇 |
1986年 | 19篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1979年 | 8篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1972年 | 3篇 |
1971年 | 6篇 |
1970年 | 3篇 |
1969年 | 5篇 |
1968年 | 7篇 |
1967年 | 6篇 |
排序方式: 共有775条查询结果,搜索用时 125 毫秒
51.
52.
The rising atmospheric CO2 concentration ([CO2]) can increase crop productivity, but there are likely to be intraspecific variations in the response. To meet future world food demand, screening for genotypes with high [CO2] responsiveness will be a useful option, but there is no criterion for high [CO2] responsiveness. We hypothesized that the Finlay–Wilkinson regression coefficient (RC) (for the relationship between a genotype's yield versus the mean yield of all genotypes in a specific environment) could serve as a pre‐screening criterion for identifying genotypes that respond strongly to elevated [CO2]. We collected datasets on the yield of 6 rice and 10 soybean genotypes along environmental gradients and compared their responsiveness to elevated [CO2] based on the regression coefficients (i.e. the increases of yield per 100 µmol mol?1 [CO2]) identified in previous reports. We found significant positive correlations between the RCs and the responsiveness of yield to elevated [CO2] in both rice and soybean. This result raises the possibility that the coefficient of the Finlay–Wilkinson relationship could be used as a pre‐screening criterion for [CO2] responsiveness. 相似文献
53.
54.
Bacterial flagellar motors are molecular machines powered by the electrochemical potential gradient of specific ions across the membrane. Bacteria move using rotating helical flagellar filaments. The flagellar motor is located at the base of the filament and is buried in the cytoplasmic membrane. Flagellar motors are classified into two types according to the coupling ion: namely the H(+)-driven motor and the Na(+)-driven motor. Analysis of the flagellar motor at the molecular level is far more advanced in the H(+)-driven motor than in the Na(+)-driven motor. Recently, the genes of the Na(+)-driven motor have been cloned from a marine bacterium of Vibrio sp. and some of the motor proteins have been purified and characterized. In this review, we summarize recent studies of the Na(+)-driven flagellar motor. 相似文献
55.
Intervention of thymus and activation-regulated chemokine attenuates the development of allergic airway inflammation and hyperresponsiveness in mice 总被引:17,自引:0,他引:17
Kawasaki S Takizawa H Yoneyama H Nakayama T Fujisawa R Izumizaki M Imai T Yoshie O Homma I Yamamoto K Matsushima K 《Journal of immunology (Baltimore, Md. : 1950)》2001,166(3):2055-2062
Thymus- and activation-regulated chemokine (TARC; CCL17) is a lymphocyte-directed CC chemokine that specifically chemoattracts CC chemokine receptor 4-positive (CCR4(+)) Th2 cells. To establish the pathophysiological roles of TARC in vivo, we investigated here whether an mAb against TARC could inhibit the induction of asthmatic reaction in mice elicited by OVA. TARC was constitutively expressed in the lung and was up-regulated in allergic inflammation. The specific Ab against TARC attenuated OVA-induced airway eosinophilia and diminished the degree of airway hyperresponsiveness with a concomitant decrease in Th2 cytokine levels. Our results for the first time indicate that TARC is a pivotal chemokine for the development of Th2-dominated experimental allergen-induced asthma with eosinophilia and AHR. This study also represents the first success in controlling Th2 cytokine production in vivo by targeting a chemokine. 相似文献
56.
To characterize the proteins involved in cell clump/cell adhesion of insect cellular defense reactions, we induced the cell clump/cell adhesion reaction in vitro with the hemolymph of larvae of the coleopteran insect, Tenebrio molitor. The 72 kDa protein was specifically enriched in the residues of cell clump/cell adhesion and was purified to homogeneity. A cDNA clone for the 72 kDa protein was isolated. We found that the 72 kDa protein was an activated phenoloxidase from Tenebrio pro-phenoloxidase. We suggest that activated phenoloxidase is involved in the cell clump/cell adhesion reaction as well as in the synthesis of melanin. 相似文献
57.
Vibrio cholerae is a highly motile bacterium which possesses a single polar flagellum as a locomotion organelle. Motility is thought to be an important factor for the virulence of V. cholerae. The genome sequencing project of this organism is in progress, and the genes that are highly homologous to the essential genes of the Na+-driven polar flagellar motor of Vibrio alginolyticus were found in the genome database of V. cholerae. The energy source of its flagellar motor was investigated. We examined the Na+ dependence and the sensitivity to the Na+ motor-specific inhibitor of the motility of the V. cholerae strains and present the evidence that the polar flagellar motor of V. cholerae is driven by an Na+ motive force. 相似文献
58.
Transient hyper-17-OHPnemia unrelated to cross-reactions with residual fetal adrenal cortex products
Mizuno H Ohro Y Sugiyama Y Ito T Hasegawa T Homma K Ueshiba H Ono M Togari H 《Hormone research》2004,61(5):242-245
OBJECTIVE: To clarify the pathogenesis of transient hyper-17alpha-hydroxyprogesteronemia, we initiated a laboratory investigation in a pre-term infant with persistently high serum 17alpha-hydroxyprogesterone (17-OHP) until 2 months of age. METHODS: Serum 17-OHP level was measured by high-performance liquid chromatography and radioimmunoassay, and gene analysis of CYP21A2 (21-hydroxylase) was performed. RESULT: Serum 17-OHP level on the 29th day of life was 25.4 ng/ml, and the urinary steroid profile showed low pregnanetriolone. Gene analysis of 21-hydroxylase disclosed no mutation, and 17-OHP normalized by 3 months of age without specific treatment. CONCLUSION: Transient elevations in 17-OHP, which do not appear related to cross-reactions with products of a residual fetal adrenal cortex, may occur in the first few months of life. 相似文献
59.
Age-related changes of elements and relationships among elements in the common bile and pancreatic ducts 总被引:1,自引:0,他引:1
Tohno Y Tohno S Yamada MO Azuma C Moriwake Y Minami T Maruyama H Omura T 《Biological trace element research》2004,101(1):47-60
To elucidate compositional changes of the common bile and main pancreatic ducts with aging, the authors investigated age-related
changes of element contents in the common bile and pancreatic ducts by inductively coupled plasma-atomic emission spectrometry.
After ordinary dissection by medical students was finished, the common bile ducts and main pancreatic ducts (pancreatic ducts)
were resected and the element contents were determined. The Mg content increased significantly only in the pancreatic duct
with aging, but the other element contents did not change significantly in both the common bile and pancreatic ducts with
aging. Regarding the relationship among the elements, significant direct correlations were found among the contents of Ca,
P, S, and Mg in the common bile ducts, with some exceptions between P and either S or Mg contents. In the pancreatic ducts,
significant direct correlations were found between S and Mg contents and between P and Na contents. The relationships in the
elements between the common bile and pancreatic ducts were examined. It was found that there were significant direct correlations
in the Ca, Mg, and Fe contents between the common bile and pancreatic ducts; that is, as Ca, Mg, and Fe increased in the common
bile duct, they increased simultaneously in the pancreatic duct. 相似文献
60.
Izumizaki M Tamaki M Suzuki Y Iwase M Shirasawa T Kimura H Homma I 《American journal of physiology. Regulatory, integrative and comparative physiology》2003,285(4):R747-R753
The purpose of this study was to test whether chronically enhanced O2 delivery to tissues, without arterial hyperoxia, can change acute ventilatory responses to hypercapnia and hypoxia. The effects of decreased hemoglobin (Hb)-O2 affinity on ventilatory responses during hypercapnia (0, 5, 7, and 9% CO2 in O2) and hypoxia (10 and 15% O2 in N2) were assessed in mutant mice expressing Hb Presbyterian (mutation in the beta-globin gene, beta108 Asn --> Lys). O2 consumption during normoxia, measured via open-circuit methods, was significantly higher in the mutant mice than in wild-type mice. Respiratory measurements were conducted with a whole body, unrestrained, single-chamber plethysmograph under conscious conditions. During hypercapnia, there was no difference between the slopes of the hypercapnic ventilatory responses, whereas minute ventilation at the same levels of arterial PCO2 was lower in the Presbyterian mice than in the wild-type mice. During both hypoxic exposures, ventilatory responses were blunted in the mutant mice compared with responses in the wild-type mice. The effects of brief hyperoxia exposure (100% O2) after 10% hypoxia on ventilation were examined in anesthetized, spontaneously breathing mice with a double-chamber plethysmograph. No significant difference was found in ventilatory responses to brief hypoxia between both groups of mice, indicating possible involvement of central mechanisms in blunted ventilatory responses to hypoxia in Presbyterian mice. We conclude that chronically enhanced O2 delivery to peripheral tissues can reduce ventilation during acute hypercapnic and hypoxic exposures. 相似文献