全文获取类型
收费全文 | 815篇 |
免费 | 59篇 |
出版年
2023年 | 8篇 |
2022年 | 23篇 |
2021年 | 42篇 |
2020年 | 23篇 |
2019年 | 27篇 |
2018年 | 43篇 |
2017年 | 40篇 |
2016年 | 33篇 |
2015年 | 67篇 |
2014年 | 71篇 |
2013年 | 81篇 |
2012年 | 75篇 |
2011年 | 86篇 |
2010年 | 52篇 |
2009年 | 24篇 |
2008年 | 34篇 |
2007年 | 34篇 |
2006年 | 36篇 |
2005年 | 22篇 |
2004年 | 17篇 |
2003年 | 9篇 |
2002年 | 12篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1964年 | 1篇 |
1941年 | 1篇 |
1939年 | 1篇 |
1905年 | 1篇 |
排序方式: 共有874条查询结果,搜索用时 15 毫秒
781.
782.
The Apollo butterfly, Parnassius apollo (Linnaeus), was common in Europe over 100 years ago, but currently it is considered as near threatened. Different conservation programs have promoted the persistence of this species;however, it is still endangered. An example of such programs was the action devoted to reestablish the Apollo butterfly population in Pieniny National Park (Poland) from only 20-30 individuals which had survived till the last decade of the 20th century. This reintroduction has been successful;however, unexpected developmental problems appeared. Butterflies with deformed or reduced wings became frequent in the population living in the natural habitat, and particularly among those reared under seminatural conditions (in the same environment, but fenced by a net). Until recently, reasons for these malformations remained unknown. However, reports published during last months indicated that there are genetic, biochemical, and microbiological factors contributing to this phenomenon. In the malformed individuals, lesions in the wingless gene and dysfunctions of laccase 1 and 2 were found to be significantly more frequent than in normal insects. A large fraction of butterflies with deformed or reduced wings was devoid of the prokaryotic symbiont Wolbachia, which was present in most normal individuals. Moreover, Yersinia pseudotuberculosis (Pfeiffer) Smith and Thai, and Serratia sp., bacteria pathogenic to insects, were detected in the biological material from both normal and malformed butterflies from this population. These findings are summarized and discussed in this review, in the light of conservation of insects and restitution of their populations from a low number of individuals. 相似文献
783.
Katarzyna Hodyra-Stefaniak Karolina Lahutta Joanna Majewska Zuzanna Kaźmierczak Dorota Lecion Marek Harhala Weronika Kęska Barbara Owczarek Ewa Jończyk-Matysiak Anna Kłopot Paulina Miernikiewicz Dominika Kula Andrzej Górski Krystyna Dąbrowska 《Microbial biotechnology》2019,12(4):730-741
Bacteriophages draw scientific attention in medicine and biotechnology, including phage engineering, widely used to shape biological properties of bacteriophages. We developed engineered T4-derived bacteriophages presenting seven types of tissue-homing peptides. We evaluated phage accumulation in targeted tissues, spleen, liver and phage circulation in blood (in mice). Contrary to expectations, accumulation of engineered bacteriophages in targeted organs was not observed, but instead, three engineered phages achieved tissue titres up to 2 orders of magnitude lower than unmodified T4. This correlated with impaired survival of these phages in the circulation. Thus, engineering of T4 phage resulted in the short-circulating phage phenotype. We found that the complement system inactivated engineered phages significantly more strongly than unmodified T4, while no significant differences in phages’ susceptibility to phagocytosis or immunogenicity were found. The short-circulating phage phenotype of the engineered phages suggests that natural phages, at least those propagating on commensal bacteria of animals and humans, are naturally optimized to escape rapid neutralization by the immune system. In this way, phages remain active for longer when inside mammalian bodies, thus increasing their chance of propagating on commensal bacteria. The effect of phage engineering on phage pharmacokinetics should be considered in phage design for medical purposes. 相似文献
784.
The essential oils from needles, twigs, bark, wood, cones and young shoots of Pinus mugo were analyzed by GC, GC/MS, and 1H‐NMR spectroscopy. More than 130 compounds were identified. The oils differed in the quantitative composition. The principal components of the oil from twigs with needles were 3‐carene (23.8 %), myrcene (22.3 %), and α‐pinene (10.3 %). The needle oil contained mainly α‐pinene (18.6 %), 3‐carene (11.3 %), and bornyl acetate (8.3 %). The oils from twigs without needles, young shoots, bark, and wood were dominated by 3‐carene (28.6 %, 15.0 %, 18.5 %, and 34.6 %, respectively) and myrcene (23.4 %, 24.0 %, 24.6 %, and 9.4 %, respectively). In the cone oil (E)‐β‐caryophyllene was the main constituent (24.0 %). 相似文献
785.
Karolina Kordek Lixue Jiang Kaicai Fan Zhengju Zhu Li Xu Mohammad Al‐Mamun Yuhai Dou Shan Chen Porun Liu Huajie Yin Piotr Rutkowski Huijun Zhao 《Liver Transplantation》2019,9(4)
A flexible air electrode (FAE) with both high oxygen electrocatalytic activity and excellent flexibility is the key to the performance of various flexible devices, such as Zn–air batteries. A facile two‐step method, mild acid oxidation followed by air calcination that directly activates commercial carbon cloth (CC) to generate uniform nanoporous and super hydrophilic surface structures with optimized oxygen‐rich functional groups and an enhanced surface area, is presented here. Impressively, this two‐step activated CC (CC‐AC) exhibits superior oxygen electrocatalytic activity and durability, outperforming the oxygen‐doped carbon materials reported to date. Especially, CC‐AC delivers an oxygen evolution reaction (OER) overpotential of 360 mV at 10 mA cm?2 in 1 m KOH, which is among the best performances of metal‐free OER electrocatalysts. The practical application of CC‐AC is presented via its use as an FAE in a flexible rechargeable Zn–air battery. The bendable battery achieves a high open circuit voltage of 1.37 V, a remarkable peak power density of 52.3 mW cm?3 at 77.5 mA cm?3, good cycling performance with a small charge–discharge voltage gap of 0.98 V and high flexibility. This study provides a new approach to the design and construction of high‐performance self‐supported metal‐free electrodes. 相似文献
786.
Karolina Augustyniak Karolina Chrabaszcz Agnieszka Jasztal Marta Smeda Guillermo Quintas Julia Kuligowski Katarzyna M. Marzec Kamilla Malek 《Journal of biophotonics》2019,12(4)
Using high definition (HD) and ultra‐high definition (UHD) of Fourier‐transform infrared (FTIR) spectroscopic imaging, we characterized spectrally pulmonary metastases in a murine model of breast cancer comparing them with histopathological results (Hematoxylin and eosin [H&E] staining). This comparison showed excellent agreement between the methods in case of localization of metastases with size below 1 mm and revealed that label‐free HD and UHD IR spectral histopathology distinguish the type of neoplastic cells. We primary focused on differentiation between metastatic foci in the pleural cavity from cancer cells present in lung parenchyma and inflamed cells present in extracellular matrix of lungs due to growing of advanced metastases. In addition, a combination of unsupervised clustering and IR imaging indicated the high sensitivity of FTIR spectroscopy to identify chemical features of small macrometastases located under the pleural cavity and during epithelial‐mesenchymal transition. FTIR‐based spectral histopathology was proved to detect not only phases of breast cancer metastasis to lungs but also to differentiate various origins of metastases seeded from breast cancer. 相似文献
787.
Devesh Mishra Jennifer E. Richard Ivana Maric Begona Porteiro Martin Häring Sander Kooijman Saliha Musovic Kim Eerola Lorena López-Ferreras Eduard Peris Katarzyna Grycel Olesya T. Shevchouk Peter Micallef Charlotta S. Olofsson Ingrid Wernstedt Asterholm Harvey J. Grill Ruben Nogueiras Karolina P. Skibicka 《Cell reports》2019,26(11):3011-3026.e5
788.
Temperature- and hydration-dependent protein dynamics in photosystem II of green plants studied by quasielastic neutron scattering 总被引:4,自引:0,他引:4
Pieper J Hauss T Buchsteiner A Baczyński K Adamiak K Lechner RE Renger G 《Biochemistry》2007,46(40):11398-11409
Protein dynamics in hydrated and vacuum-dried photosystem II (PS II) membrane fragments from spinach has been investigated by quasielastic neutron scattering (QENS) in the temperature range between 5 and 300 K. Three distinct temperature ranges can be clearly distinguished by active type(s) of protein dynamics: (A) At low temperatures (T < 120 K), the protein dynamics of both dry and hydrated PS II is characterized by harmonic vibrational motions. (B) In the intermediate temperature range (120 < T < 240 K), the total mean square displacement total slightly deviates from the predicted linear behavior. The QENS data indicate that this deviation, which is virtually independent of the extent of hydration, is due to a partial onset of diffusive protein motions. (C) At temperatures above 240 K, the protein flexibility drastically changes because of the onset of diffusive (large-amplitude) protein motions. This dynamical transition is clearly hydration-dependent since it is strongly suppressed in dry PS II. The thermally activated onset of protein flexibility as monitored by QENS is found to be strictly correlated with the temperature-dependent increase of the electron transport efficiency from Q(A)(-) to QB (Garbers et al. (1998) Biochemistry 37, 11399-11404). Analogously, the freezing of protein mobility by dehydration in dry PS II appears to be responsible for the blockage of Q(A)(-) reoxidation by Q(B) at hydration values lower than 45% r.h. (Kaminskaya et al. (2003) Biochemistry 42, 8119-8132). Similar effects were observed for reactions of the water-oxidizing complex as outlined in the Discussion section. 相似文献
789.
Kasprzak A Adamek A Biczysko W Seidel J Przybyszewska W Olejniczak K Juszczyk J Zabel M 《Folia histochemica et cytobiologica / Polish Academy of Sciences, Polish Histochemical and Cytochemical Society》2007,45(4):357-366
Hepatitis C virus (HCV) continues to represent the main causative agent of the hepatitis, which leads to chronic transformation of the process in 60-80% individuals. It remains unclear how far cellular expression of HCV proteins in vivo may represent an index of progression of the disease and of proliferative activity in the liver in chronic hepatitis C. Aim of the studies included detection and subcellular localization of three HCV proteins (NS3, NS5A and C) in liver biopsies from adults (n=19) with chronic, long lasting hepatitis C as related to hepatocyte proliferative activity. The immunocytochemical ABC (avidin biotin-peroxidase complex) technique was applied, alone or associated with the ImmunoMax technique. Results of the immunocytochemical tests were compared to histological alterations in liver biopsies, proliferation index and with selected clinical data. A significantly higher expression of NS3 protein was noted, as compared to expressions of NS5A and C proteins. In all the patients, cytoplasmic localization of all proteins dominated over nuclear localization (p0.05). At the level of electron microscopy, protein localization in endoplasmic reticulum (ER) membranes, mitochondria, perinuclear region and/or in hepatocyte cell nucleus was observed. No direct relationships could be demonstrated between expressions of HCV proteins and of Ki-67 antigen. No correlations could also be demonstrated between cellular expression of any HCV protein on one hand and grading or staging, alanine transaminase (ALT), serum level of HCV RNA or alpha-fetoprotein (AFP) on the other. However, positive correlations were disclosed between proliferative activity of hepatocytes on one hand and patient's age, grading and staging on the other. Advanced hepatic fibrosis correlated also with serum levels of AFP. The studies were supplemented with data on subcellular localization of HCV proteins. Moreover, they indicated that in HCV infection grading and staging, proliferative activity of hepatocytes and serum AFP level represent more valuable indices of the disease progress than those provided by cellular expression of three potentially oncogenic HCV proteins in vivo. 相似文献
790.
Cieśliński H Białkowska AM Długołecka A Daroch M Tkaczuk KL Kalinowska H Kur J Turkiewicz M 《Archives of microbiology》2007,188(1):27-36
A psychrotrophic bacterium producing a cold-adapted esterase upon growth at low temperatures was isolated from the alimentary tract of Antarctic krill Euphasia superba Dana, and classified as Pseudoalteromonas sp. strain 643A. A genomic DNA library of strain 643A was introduced into Escherichia coli TOP10F', and screening on tributyrin-containing agar plates led to the isolation of esterase gene. The esterase gene (estA, 621 bp) encoded a protein (EstA) of 207 amino acid residues with molecular mass of 23,036 Da. Analysis of the amino acid sequence of EstA suggests that it is a member of the GDSL-lipolytic enzymes family. The purification and characterization of native EstA esterase were performed. The enzyme displayed 20-50% of maximum activity at 0-20 degrees C. The optimal temperature for EstA was 35 degrees C. EstA was stable between pH 9 and 11.5. The enzyme showed activity for esters of short- to medium-chain (C(4) and C(10)) fatty acids, and exhibited no activity for long-chain fatty acid esters like that of palmitate and stearate. EstA was strongly inhibited by phenylmethylsulfonyl fluoride, 2-mercaptoethanol, dithiothreitol and glutathione. Addition of selected divalent ions e.g. Mg(2+), Co(2+) and Cu(2+) led to the reduction of enzymatic activity and the enzyme was slightly activated ( approximately 30%) by Ca(2+) ions. 相似文献