全文获取类型
收费全文 | 4023篇 |
免费 | 352篇 |
国内免费 | 2篇 |
出版年
2023年 | 14篇 |
2022年 | 31篇 |
2021年 | 81篇 |
2020年 | 46篇 |
2019年 | 48篇 |
2018年 | 59篇 |
2017年 | 61篇 |
2016年 | 96篇 |
2015年 | 219篇 |
2014年 | 182篇 |
2013年 | 240篇 |
2012年 | 357篇 |
2011年 | 294篇 |
2010年 | 196篇 |
2009年 | 128篇 |
2008年 | 218篇 |
2007年 | 248篇 |
2006年 | 203篇 |
2005年 | 209篇 |
2004年 | 219篇 |
2003年 | 194篇 |
2002年 | 183篇 |
2001年 | 31篇 |
2000年 | 25篇 |
1999年 | 30篇 |
1998年 | 84篇 |
1997年 | 29篇 |
1996年 | 40篇 |
1995年 | 36篇 |
1994年 | 40篇 |
1993年 | 28篇 |
1992年 | 32篇 |
1991年 | 23篇 |
1990年 | 30篇 |
1989年 | 36篇 |
1988年 | 20篇 |
1987年 | 18篇 |
1986年 | 21篇 |
1985年 | 23篇 |
1984年 | 33篇 |
1983年 | 30篇 |
1982年 | 38篇 |
1981年 | 26篇 |
1980年 | 30篇 |
1979年 | 21篇 |
1978年 | 11篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1974年 | 14篇 |
1973年 | 9篇 |
排序方式: 共有4377条查询结果,搜索用时 203 毫秒
21.
Jacqueline Cramer 《Aquatic Ecology》1985,19(2):207-216
Due to the rise of environmental concern ecologists have been asked for advice more frequently since the late 1960s. This article discusses how the changing relationship between ecologists and society has affected the behaviour of one particular group of ecologists, namely Dutch fresh water ecologists, by focussing on their behaviour towards job market control and public interest activities. The analysis has been based on interviews with 65 Dutch fresh water ecologists together with an analysis of their publications.In contrast with American ecologists, Dutch fresh water ecologists have made little effort to control their job market by formal arrangements such as formulating a code of ethics and certification procedures. Secondly, Dutch fresh water ecologists generally conceive of their own role in contributing to the solution of environmental problems in relation to that of the environmentalists by doing good research and reliable advisory work. Although a significant number of researchers also address lay publics by writing popular articles and/or holding lectures, only a minority actively participates in environmental politics. 相似文献
22.
Respiratory chain phosphorylation has been investigated in the methylotrophic bacterium Methylophilus methylotrophus following the addition of oxidisable substrates to aerobic, whole cell suspensions. Initial-rate experiments showed that ATP synthesis occurred at the overall expense of AMP and inorganic phosphate via the sequential action of the ATP phosphohydrolase and adenylate kinase; some of the nascent ATP was rapidly used to synthesis nonadenine nucleoside triphosphates. After being corrected for ATP turnover, Pi/O quotients of 0.46 to 0.54, 0.77 and 1.37 nmol/ng-atom O were obtained for the oxidation of methanol dehydrogenase-linked substrates (methanol, ethanol and acetaldehyde), duroquinol and formate (NAD+-linked) respectively. These values were proportional to the H+/O and/or K+/O quotients exhibited by these substrates, and yielded an average H+/ATP (H+/Pi) quotient of 4.2 ng-ion H+/nmol. Steady-state experiments showed that the extent of cellular energisation varied with the respiration rate but was always in the order methanol > duroquinol > acetaldehyde, thus indicating that under these longer-term conditions methanol was completely oxidised to yield PQQH2 and 2NAD(P)H. These results are discussed in terms of the various reactions which lead to the generation or utilisation of the protonmotive force in this organism.Abbreviations FCCP
carbonylcyanide p-trifluoromethyxyphenyl-hydrazone
-
bulk phase, transmembrane electrochemical potential difference of protons (
)
- pH
bulk phase, transmembrane pH difference (pHin–pHout)
-
bulk phase, transmembrane electrical potential difference (in - out)
- [P]
concentration of anhydride phosphate bonds in adenine nucleotides (2[ATP]+[ADP])
- FPLC
fast protein liquid chromatography
- PQQ
pyrroloquinoline quinone
- Gp
phosphorylation potential 相似文献
23.
Chardonnet Yvette Viac Jacqueline Levai Jacques Begoud Gérard Morgon Alain Thivolet Jean 《Virchows Archiv. B, Cell pathology including molecular pathology》1986,51(1):421-428
Virchows Archiv B Cell Pathology - Various parameters of the local cellular response have been studied in 16 laryngeal papillomas from ten patients with recurrent papillomas as well as normal... 相似文献
24.
Franz Bogner Michael Boppré Klaus-Dieter Ernst Jürgen Boeckh 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1986,158(6):741-749
Summary The tips of the labial palps ofRhodogastria possess a pit housing uniform sensilla (Fig. 1), histologically characterized by wall-pores and receptor cells with lamellated outer dendrites (Fig. 2). The receptor cell axons project to glomeruli in the deutocerebrum (cf. Fig. 3) which are not innervated by antennal receptors. From their histology as well as from their central projection these sense organs are identical with palpal pit organs of other Lepidoptera (Lee et al. 1985; Kent et al. 1986; Lee and Altner 1986).Physiologically, the palp-pit receptors respond uniformly; they are most excitable by stimulation with carbon dioxide (Fig. 6) while they exhibit relatively moderate responses to various odorants (Fig. 4). The responses to CO2 (Fig. 7) show a steep dose-response characteristic. In ambient atmosphere (i.e., ca. 0.03% CO2) the cells are in an excited condition already; the seeming spontaneous activity exhibited in air is decreased if the preparation is kept under N2 or O2 or CO2-free air (Figs. 7, 10). There is hardly any adaptation of the responses to continuous or repeated stimulation (Fig. 8). Perhaps CO2 sensitivity is correlated with sensilla characterized by both wall-pores and lamellated dendrites. Pilot tests indicate that CO2 perception might be widespread in the Lepidoptera (cf. Fig. 12), but the biological significance remains obscure. 相似文献
25.
A chronic intoxication with carbaryl, fenthion and lindane was induced in young snails. The parameter k of the von Bertalanffy's equation showed clearly the growth changes induced by these insecticides. In all cases the fecundity of intoxicated snails was reduced. Among these three insecticides, lindane was the most toxic, carbaryl the least. 相似文献
26.
Acute toxicity and degradation of an aqueous suspension of Thiram were studied in Cloeon dipterum. Lethal concentrations for 50% of the larvae (LC 50) after 24 to 96 h of exposure and thresholds were calculated. LC 50 varied from 0.39 to 1.92 mg·l?1 according to the time and the physiological state of the larvae. It was demonstrated that: the sensitivity of the larvae increased with the time during which they were kept in the laboratory; while the toxicity of the aqueous suspension (1 mg·l?1) of Thiram decreased with time, another toxic product was formed. 相似文献
27.
Levels of immunoreactive pro-opiomelanocortin (POMC) peptides (N- and C-terminal ACTH, N- and C-terminal LPH and α-MSH) have been measured in pituitary extracts from human fetuses of 12–22 weeks gestation. The levels of ACTH were 30–200 times higher than α-MSH in all fetuses studied. Sephadex G-75 and G-25 chromatography of 8 extracts showed peaks of 34 kilodaltons (K) POMC, 22K ACTH, β-LPH, γ-LPH, β-endorphin, approximately 8K ACTH, 1–39 ACTH, α-MSH and CLIP. The 8K and 22K forms of ACTH are both partly glycosylated.In vitro culture of pituitaries from 2 fetuses (22 and 26 weeks gestation) gave a detectable basal output of ACTH but not of α-MSH. Stimulation of these pituitary cells with human fetal and rat hypothalamic extracts and with synthetic ovine CRF-41 produced a significant increase in ACTH release, and either small or undetectable amounts of α-MSH.These results demonstrate the presence of POMC-related peptides in early gestation human fetal pituitaries and suggest that ACTH, and not α-MSH, is the major corticotrophic hormone at this stage of gestation. 相似文献
28.
Charnley low-friction arthroplasty was performed on 352 osteoarthritic hips, usually because of severe pain. Three hundred and twenty hips were reviewed at a special follow-up clinic or by postal questionnaire. After operation 89% of hips were pain-free or caused only occasional discomfort, and in 76% there was an increased range of movement. Of those patients actually seen for review 79% were judged to have a good or excellent result. The most frequent single complication was deep infection, which occurred in 5·3% of hips. 相似文献
29.
30.