全文获取类型
收费全文 | 3535篇 |
免费 | 435篇 |
国内免费 | 169篇 |
出版年
2023年 | 91篇 |
2022年 | 77篇 |
2021年 | 128篇 |
2020年 | 149篇 |
2019年 | 145篇 |
2018年 | 149篇 |
2017年 | 126篇 |
2016年 | 165篇 |
2015年 | 134篇 |
2014年 | 188篇 |
2013年 | 259篇 |
2012年 | 148篇 |
2011年 | 260篇 |
2010年 | 143篇 |
2009年 | 194篇 |
2008年 | 180篇 |
2007年 | 167篇 |
2006年 | 144篇 |
2005年 | 128篇 |
2004年 | 134篇 |
2003年 | 99篇 |
2002年 | 94篇 |
2001年 | 82篇 |
2000年 | 56篇 |
1999年 | 51篇 |
1998年 | 58篇 |
1997年 | 52篇 |
1996年 | 53篇 |
1995年 | 61篇 |
1994年 | 42篇 |
1993年 | 48篇 |
1992年 | 28篇 |
1991年 | 30篇 |
1990年 | 22篇 |
1989年 | 23篇 |
1988年 | 19篇 |
1987年 | 11篇 |
1986年 | 16篇 |
1985年 | 17篇 |
1984年 | 26篇 |
1983年 | 22篇 |
1982年 | 27篇 |
1981年 | 16篇 |
1980年 | 11篇 |
1979年 | 14篇 |
1978年 | 5篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1973年 | 7篇 |
排序方式: 共有4139条查询结果,搜索用时 15 毫秒
1.
Water pollution from industrial Metro Łódź (ML), Poland, made the Ner River almost fishless in its middle-lower course for most of the 19th and 20th century. The new sewage treatment plant of ML and reduction of industry have caused pollution abatement there since the 1990s. As a result, the Ner became repopulated, which was shown by fish samples collected along its course in 2000–2012. Multivariate statistical methods helped distinguish unpolluted (I and II, in the upper course), and recovered (III, IV and V, in the middle-lower course) sections of the river. Historical and present data indicated that section III (downstream of ML) recovered least, both before and during the study. Section V (outflow one) recovered most and its fish fauna (almost exclusively native) now displays high and stable biomass, abundance and species richness, including those of obligatory riverine species. Non-native Prussian carp's dominance followed the river degradation gradient, i.e. was highest in section III, and in section V declined to almost absence. This study shows that the revival of native fish fauna seems to be a method of restricting the dominance of this highly tolerant species. Despite the abatement, storm events are very harmful to fish (mostly in section III), because the Ner discharge may then increase manifold and all storm water is drained by the ML combined sewer system to the Ner in several hours. Other stressors are numerous dams and desorption of pollutants from sediment in the middle Ner, and perhaps pollutant inflow from agriculture or local urban areas. Some moderation of storm impact on water entering the Ner from ML by constructing buffer reservoirs would probably cause further fish recovery in section III. 相似文献
2.
Stamatia Bellou Mohammed N. Baeshen Ahmed M. Elazzazy Dimitra Aggeli Fotoon Sayegh George Aggelis 《Biotechnology advances》2014
In the last few years, there has been an intense interest in using microalgal lipids in food, chemical and pharmaceutical industries and cosmetology, while a noteworthy research has been performed focusing on all aspects of microalgal lipid production. This includes basic research on the pathways of solar energy conversion and on lipid biosynthesis and catabolism, and applied research dealing with the various biological and technical bottlenecks of the lipid production process. In here, we review the current knowledge in microalgal lipids with respect to their metabolism and various biotechnological applications, and we discuss potential future perspectives. 相似文献
3.
The effects of cold treatment on the cortical microtubules (MTs) of Chaetomorpha moniligera Kjellman were investigated by immunofluorescence microscopy. Cortical MTs in Chaetomorpha thallus are arranged longitudinally. In this study, 70–75% of MTs disassembled within 4 h on ice while the others remained stable under these conditions. Reticulate background immunofluorescence, assumed to indicate the presence of a tubulin monomer, was distributed about the stable MTs. Immunofluorescence was prominent in only 50% of the cells. Tubulin polymerization was noted where the background and MT immunofluorescence was strong. New MTs grew transversely as single strings or clusters from the sides of MTs after cold treatment for 4 h and elongated with time to take on a reticulate form at 24 h. The significance of this tubulin polymerization under cold treatment is discussed.Abbreviations MT
microtubule
- MTOC
microtubule-organizing center 相似文献
4.
Biochemical Study on the Critical Period for Treatment of the Mottled Brindled Mouse 总被引:2,自引:0,他引:2
Hemizygous mottled brindled mice (Mobr/y mice) were treated by subcutaneous injection of copper and were decapitated on postnatal day 14. Cytochrome c oxidase (COX) activity of the brain mitochondria in the mice given 10 micrograms of copper/g on day 4 or 7 showed significant increases compared with that of untreated Mobr/y animals, and these mice had no neurological symptoms. Mice given 10 micrograms of copper/g on day 12 showed neither increases in COX activity nor clinical improvement. The brain levels of copper, noradrenaline, and dopamine in the mice treated on day 12 were the same as those in animals treated on day 4 or 7. The in vitro activities of dopamine-beta-hydroxylase of the brain were also the same among the treated mice, irrespective of the date of treatment. The results indicate that delays in copper treatment produce irreversible changes in COX activity of the brain and lead to clinical unresponsiveness to treatment. 相似文献
5.
Matineh Barati Bagherabad Fahimeh Afzaljavan Soodabeh ShahidSales Seyed Mahdi Hassanian Amir Avan 《Journal of cellular biochemistry》2019,120(3):2726-2741
Pancreatic ductal adenocarcinoma (PDAC) is an incidence rate nearly equal to its mortality rate. The poor prognosis of the disease can be explained by the absence of effective biomarkers for screening and early detection, together with the aggressive behavior and resistance to the currently available chemotherapy. The therapeutic failure can also be attributed to the inter-/intratumor genetic heterogeneity and the abundance of tumor stroma that occupies the majority of the tumor mass. Gemcitabine is used in the treatment of PDAC; however, the response rate is less than 12%. A recent phase III trial revealed that the combination of oxaliplatin, irinotecan, fluorouracil, and leucovorin could be an option for the treatment of metastatic PDAC patients with good performance status, although these approaches can result in high toxicity level. Further investigations are required to develop innovative anticancer agents that either improve gemcitabine activity, within novel combinatorial approaches or acts with a better efficacy than gemcitabine. The aim of the current review is to give an overview of preclinical and clinical studies targeting key dysregulated signaling pathways in PDAC. 相似文献
6.
Olive oil history,production and by-product management 总被引:1,自引:0,他引:1
Iosif Emmanouil Kapellakis Konstantinos P. Tsagarakis John C. Crowther 《Reviews in Environmental Science and Biotechnology》2008,7(1):1-26
In this review paper, the history of the olive tree and the development of the main olive oil extraction systems employed
in the past are presented. Furthermore, the management techniques employed from antiquity until today for the treatment of
olive mill wastewater (OMW), which constitutes the most important by-product of olive oil production, are addressed and compared.
Reference is also made to global olive oil production, the environmental impacts of the uncontrolled disposal of OMW, and
to the legal framework concerning its management in the main olive oil producing countries. Other by-products of olive processing
are also discussed. 相似文献
7.
8.
Animal-assisted therapies (AATs) are not widely promoted in routine mental healthcare but represent a viable treatment option given positive perceptions of pets and growing evidence that animals provide meaningful contribution to psychological wellbeing. Relatively little is known about the general public's attitude toward AATs, especially in relation to more commonly used alternatives. This study compared the acceptability of four different treatment options (AAT, medication, psychotherapy, and no active treatment) for common externalizing behaviors in children. Parents from a community sample (N = 189) were presented with vignettes describing a child with symptoms of an externalizing behavior disorder and were asked to rate the acceptability of the four different treatment options. Participants rated AAT as a highly acceptable form of treatment and more acceptable than no active treatment and medication. However, AAT was rated as less acceptable than psychotherapy. Experiences with animals (both positive and negative) were unrelated to the acceptability of AAT. These findings suggest that AAT is viewed as a highly acceptable form of treatment for common externalizing behaviors and should be more systematically investigated as a treatment for children's mental health problems. 相似文献
9.
Huan-Chen Li Chitra Mani David Kupfer 《Journal of biochemical and molecular toxicology》1993,8(4):195-206
Methoxychlor, a currently used pesticide, is demethylated and hydroxylated by several hepatic microsomal cytochrome P450 enzymes. Also, methoxychlor undergoes metabolic activation, yielding a reactive intermediate (M*) that binds irreversibly and apparently covalently to microsomal proteins. The study investigated whether methoxychlor could inhibit or inactivate certain liver microsomal P450 enzymes. The regioselective and stereoselective hydrox-ylation of testosterone and the 2-hydroxylation of estradiol (E2) were utilized as markers of the P450 enzymes inhibited by methoxychlor. Both reversible and time-dependent inhibition were examined. Coincubation of methoxychlor and testosterone with liver microsomes from phenobarbital treated (PB-microsomes) male rats, yielded marked diminution of 2α- and 16α-testosterone hydroxylation, indicating strong inhibition of P4502C11 (P450h). Methoxychlor moderately inhibited 2β-, 7α-, 15α-, 15β-, and 16β-hydroxylation and androstenedi-one formation. There was only a weak inhibition of 6β-ydroxylation of testosterone. The methox-ychlor-mediated inhibition of 6β-hydroxylation was competitive. By contrast, when methoxychlor was permitted to be metabolized by PB-microsomes or by liver microsomes from pregnenolone-16α-car-bonitrile treated rats (PCN-microsomes) prior to addition of testosterone, a pronounced time-dependent inhibition of 6β-hydroxylation was observed, suggesting that methoxychlor inactivates the P450 3A isozyme(s). The di-demethylated methoxychlor (bis-OH-M) and the tris-hydroxy (ca-techol) methoxychlor metabolite (tris-OH-M) inhibited 6β-hydroxylation in PB-microsomes competitively and noncompetitively, respectively; however, these methoxychlor metabolites did not exhibit a time-dependent inhibition. Methoxychlor inhibited competitively the formation of 7α-hydroxytestosterone (7α-OH-T) and 16α-hydroxy-testosterone (16α-OH-T) but exhibited little or no time-dependent inhibition of generation of these metabolites, indicating that P450s 2A1, 2B1/B2, and 2C11 were inhibited but not inactivated. Methoxychlor inhibited in a time-dependent fashion the 2-hydroxylation of E2 in PB-microsomes. However, bis-OH-M exhibited solely reversible inhibition of the 2-hydroxylation, supporting our conclusion that the inactivation of P450s does not involve participation of the demethylated metabolites. Both competitive inhibition and time-dependent inactivation of human liver P450 3A (6β-hydroxylase) by methoxychlor, was observed. As with rat liver microsomes, the human 6β-hydroxylase was inhibited by bis-OH-M and tris-OH-M competitively and noncompetitively, respectively. Testosterone and estradiol strongly inhibited the irreversible binding of methoxychlor to microsomal proteins. This might explain the “clean” competitive inhibition by methoxychlor of the 6β-OH-T formation when the compounds were coin-cubated. Glutathione (GSH) has been shown to interfere with the irreversible binding of methoxychlor to PB-microsomal proteins. The finding that the coincubation of GSH with methoxychlor partially diminishes the time-dependent inhibition of 6β-hydroxylation provides supportive evidence that the inactivation of P450 3A isozymes by methoxychlor is related to the formation of M*. 相似文献
10.